Remove jetty server dependency in http_servlet. (#1685)

Author: rghetia

contrib/http_servlet/build.gradle

@@ -9,14 +9,11 @@ description = 'OpenCensus Http Servlet Plugin'
     it.targetCompatibility = 1.6
 }
 
-def jettyVersion = "9.2.25.v20180606"
-
 dependencies {
     compile project(':opencensus-api')
     compile project(':opencensus-contrib-http-util')
 
-    compile "javax.servlet:javax.servlet-api:3.0.1",
-            "org.eclipse.jetty:jetty-server:${jettyVersion}"
+    compile "javax.servlet:javax.servlet-api:3.0.1"
 
     signature "org.codehaus.mojo.signature:java17:1.0@signature"
     signature "net.sf.androidscents.signature:android-api-level-14:4.0_r4@signature"

contrib/http_servlet/src/main/java/io/opencensus/contrib/http/servlet/OcHttpServletUtil.java

@@ -20,7 +20,6 @@
 import io.opencensus.contrib.http.HttpServerHandler;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
-import org.eclipse.jetty.server.Response;
 
 class OcHttpServletUtil {
   static final String CONTENT_LENGTH = "Content-Length";
@@ -39,11 +38,6 @@ static void recordMessageSentEvent(
         } catch (NumberFormatException e) {
           return;
         }
-      } else {
-        if (response instanceof Response) {
-          Response resp = (Response) response;
-          handler.handleMessageSent(context, resp.getContentCount());
-        }
       }
     }
   }