bigtable: delete unnecessary test class (#3342)

The file was copied from gax to help test BigTable.
However, the deleted class isn't actually used anywhere,
and will fail to compile when we update gax to stabilize bidi-streaming
API.

This commit simply deletes the problematic class. If we need it later to
test BigTable, we can just copy it again.
In this way, we don't need to go through the complicated breaking-change
release process.

google-cloud-clients/google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/gaxx/testing/FakeStreamingApi.java

@@ -19,7 +19,6 @@
 import com.google.api.gax.rpc.ApiCallContext;
 import com.google.api.gax.rpc.ApiExceptionFactory;
 import com.google.api.gax.rpc.ApiStreamObserver;
-import com.google.api.gax.rpc.BidiStreamingCallable;
 import com.google.api.gax.rpc.ClientStreamingCallable;
 import com.google.api.gax.rpc.ResponseObserver;
 import com.google.api.gax.rpc.ServerStreamingCallable;
@@ -36,84 +35,6 @@
 
 @InternalApi("for testing")
 public class FakeStreamingApi {
-
-  public static class BidiStreamingStashCallable<RequestT, ResponseT>
-      extends BidiStreamingCallable<RequestT, ResponseT> {
-    private ApiCallContext context;
-    private ApiStreamObserver<ResponseT> responseObserver;
-    private AccumulatingStreamObserver<RequestT> requestObserver;
-    private List<ResponseT> responseList;
-
-    public BidiStreamingStashCallable() {
-      responseList = new ArrayList<>();
-    }
-
-    public BidiStreamingStashCallable(List<ResponseT> responseList) {
-      this.responseList = responseList;
-    }
-
-    @Override
-    public ApiStreamObserver<RequestT> bidiStreamingCall(
-        ApiStreamObserver<ResponseT> responseObserver, ApiCallContext context) {
-      Preconditions.checkNotNull(responseObserver);
-      this.responseObserver = responseObserver;
-      this.context = context;
-      this.requestObserver = new AccumulatingStreamObserver<>();
-      return requestObserver;
-    }
-
-    public ApiCallContext getContext() {
-      return context;
-    }
-
-    public ApiStreamObserver<ResponseT> getActualObserver() {
-      return responseObserver;
-    }
-
-    public List<RequestT> getActualRequests() {
-      return requestObserver.getValues();
-    }
-
-    private void sendResponses() {
-      for (ResponseT response : responseList) {
-        responseObserver.onNext(response);
-      }
-      responseObserver.onCompleted();
-    }
-
-    private class AccumulatingStreamObserver<T> implements ApiStreamObserver<T> {
-      private List<T> requestList = new ArrayList<>();
-      private Throwable error;
-      private boolean completed = false;
-
-      @Override
-      public void onNext(T value) {
-        requestList.add(value);
-      }
-
-      @Override
-      public void onError(Throwable t) {
-        error = t;
-      }
-
-      @Override
-      public void onCompleted() {
-        completed = true;
-        BidiStreamingStashCallable.this.sendResponses();
-      }
-
-      public List<T> getValues() {
-        if (!completed) {
-          throw new IllegalStateException("Stream not completed.");
-        }
-        if (error != null) {
-          throw ApiExceptionFactory.createException(error, FakeStatusCode.of(Code.UNKNOWN), false);
-        }
-        return requestList;
-      }
-    }
-  }
-
   public static class ServerStreamingStashCallable<RequestT, ResponseT>
       extends ServerStreamingCallable<RequestT, ResponseT> {
     private ApiCallContext context;