chore: mark opencensus as deprecated (googleapis#2533)

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Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: andre-sampaio

.readme-partials.yml

@@ -149,82 +149,9 @@ custom_content: |
   [CustomOpenTelemetryMetricsProvider](https://github.com/googleapis/java-bigtable/blob/main/google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/CustomOpenTelemetryMetricsProvider.java)
   on how to set it up.
 
-  ## Client request tracing: OpenCensus Tracing
-
-  Cloud Bigtable client supports [OpenCensus Tracing](https://opencensus.io/tracing/),
-  which gives insight into the client internals and aids in debugging production issues.
-  By default, the functionality is disabled. For example to enable tracing using
-  [Google Stackdriver](https://cloud.google.com/trace/docs/):
-
-  [//]: # (TODO: figure out how to keep opencensus version in sync with pom.xml)
-
-  If you are using Maven, add this to your pom.xml file
-  ```xml
-  <dependency>
-    <groupId>io.opencensus</groupId>
-    <artifactId>opencensus-impl</artifactId>
-    <version>0.31.1</version>
-    <scope>runtime</scope>
-  </dependency>
-  <dependency>
-    <groupId>io.opencensus</groupId>
-    <artifactId>opencensus-exporter-trace-stackdriver</artifactId>
-    <version>0.31.1</version>
-    <exclusions>
-      <exclusion>
-        <groupId>io.grpc</groupId>
-        <artifactId>*</artifactId>
-      </exclusion>
-      <exclusion>
-        <groupId>com.google.auth</groupId>
-        <artifactId>*</artifactId>
-      </exclusion>
-    </exclusions>
-  </dependency>
-  ```
-  If you are using Gradle, add this to your dependencies
-  ```Groovy
-  compile 'io.opencensus:opencensus-impl:0.24.0'
-  compile 'io.opencensus:opencensus-exporter-trace-stackdriver:0.24.0'
-  ```
-  If you are using SBT, add this to your dependencies
-  ```Scala
-  libraryDependencies += "io.opencensus" % "opencensus-impl" % "0.24.0"
-  libraryDependencies += "io.opencensus" % "opencensus-exporter-trace-stackdriver" % "0.24.0"
-  ```
-
-  At the start of your application configure the exporter:
-
-  ```java
-  import io.opencensus.exporter.trace.stackdriver.StackdriverTraceConfiguration;
-  import io.opencensus.exporter.trace.stackdriver.StackdriverTraceExporter;
-
-  StackdriverTraceExporter.createAndRegister(
-    StackdriverTraceConfiguration.builder()
-        .setProjectId("YOUR_PROJECT_ID")
-        .build());
-  ```
-
-  You can view the traces on the Google Cloud Platform Console
-  [Trace](https://console.cloud.google.com/traces) page.
-
-  By default traces are [sampled](https://opencensus.io/tracing/sampling) at a rate of about 1/10,000.
-  You can configure a higher rate by updating the active tracing params:
-
-  ```java
-  import io.opencensus.trace.Tracing;
-  import io.opencensus.trace.samplers.Samplers;
-
-  Tracing.getTraceConfig().updateActiveTraceParams(
-      Tracing.getTraceConfig().getActiveTraceParams().toBuilder()
-          .setSampler(Samplers.probabilitySampler(0.01))
-          .build()
-  );
-  ```
-
   ### Disable Bigtbale traces
 
-  If your application already has OpenCensus Tracing integration and you want to disable Bigtable
+  If your application already has tracing integration and you want to disable Bigtable
   traces, you can do the following:
 
   ```java

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/BigtableDataSettings.java

@@ -146,6 +146,7 @@ public static Builder newBuilderForEmulator(String hostname, int port) {
   }
 
   /**
+   * @deprecated OpenCensus support is deprecated and will be removed in a future version
    * Enables OpenCensus metric aggregations.
    *
    * <p>This will register Bigtable client relevant {@link io.opencensus.stats.View}s. When coupled
@@ -179,7 +180,7 @@ public static Builder newBuilderForEmulator(String hostname, int port) {
    *   BigtableDataSettings.enableOpenCensusStats();
    * }</pre>
    */
-  @BetaApi("OpenCensus stats integration is currently unstable and may change in the future")
+  @Deprecated
   public static void enableOpenCensusStats() {
     com.google.cloud.bigtable.data.v2.stub.metrics.RpcViews.registerBigtableClientViews();
     // TODO(igorbernstein): Enable grpc views once we upgrade to grpc-java 1.24.0
@@ -188,15 +189,14 @@ public static void enableOpenCensusStats() {
   }
 
   /**
-   * Enables OpenCensus GFE metric aggregations.
-   *
-   * <p>This will register views for gfe_latency and gfe_header_missing_count metrics.
-   *
-   * <p>gfe_latency measures the latency between Google's network receives an RPC and reads back the
-   * first byte of the response. gfe_header_missing_count is a counter of the number of RPC
-   * responses received without the server-timing header.
+   * @deprecated OpenCensus support is deprecated and will be removed in a future version Enables
+   *     OpenCensus GFE metric aggregations.
+   *     <p>This will register views for gfe_latency and gfe_header_missing_count metrics.
+   *     <p>gfe_latency measures the latency between Google's network receives an RPC and reads back
+   *     the first byte of the response. gfe_header_missing_count is a counter of the number of RPC
+   *     responses received without the server-timing header.
    */
-  @BetaApi("OpenCensus stats integration is currently unstable and may change in the future")
+  @Deprecated
   public static void enableGfeOpenCensusStats() {
     com.google.cloud.bigtable.data.v2.stub.metrics.RpcViews.registerBigtableClientGfeViews();
   }

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/RpcViews.java

@@ -15,14 +15,13 @@
  */
 package com.google.cloud.bigtable.data.v2.stub.metrics;
 
-import com.google.api.core.BetaApi;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableSet;
 import io.opencensus.stats.Stats;
 import io.opencensus.stats.View;
 import io.opencensus.stats.ViewManager;
 
-@BetaApi
+@Deprecated
 public class RpcViews {
   @VisibleForTesting
   private static final ImmutableSet<View> BIGTABLE_CLIENT_VIEWS_SET =