Refactor: Remove confusing unused internal constructor in OtlpExporterOptions

The internal constructor was only ever called from the public constructor, and the public constructor itself is only used in tests.
This made it easy to assume the internal constructor was part of normal runtime scenarios, which could cause confusion.
(in normal runtime scenarios, only the factory method `OtlpExporterOptions.CreateOtlpExporterOptions` is used)

Removing it simplifies the code and avoids misleading readers.

Author: lyra95

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/OtlpExporterOptions.cs

@@ -48,16 +48,10 @@ public class OtlpExporterOptions : IOtlpExporterOptions
     /// Initializes a new instance of the <see cref="OtlpExporterOptions"/> class.
     /// </summary>
     public OtlpExporterOptions()
-        : this(OtlpExporterOptionsConfigurationType.Default)
-    {
-    }
-
-    internal OtlpExporterOptions(
-        OtlpExporterOptionsConfigurationType configurationType)
         : this(
-              configuration: new ConfigurationBuilder().AddEnvironmentVariables().Build(),
-              configurationType,
-              defaultBatchOptions: new())
+            configuration: new ConfigurationBuilder().Build(),
+            configurationType: OtlpExporterOptionsConfigurationType.Default,
+            defaultBatchOptions: new())
     {
     }