firestore: remove test for codes.Canceled with RPC

The test is flaky and it isn't clear why. There is some nondeterminism that I can't figure out.

Change-Id: I8d4bf0b374a8e980b35892c36bb451b42e03a045
Reviewed-on: https://code-review.googlesource.com/26110
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jean de Klerk <deklerk@google.com>
diff --git a/firestore/watch_test.go b/firestore/watch_test.go
index ccae8bd..844887b 100644
--- a/firestore/watch_test.go
+++ b/firestore/watch_test.go
@@ -321,23 +321,6 @@
 	_, _, _, err = ws.nextSnapshot()
 	codeEq(t, "cancel from gax.Sleep", codes.Canceled, err)
 
-	// Cancel from an RPC.
-	ctx2, cancel = context.WithCancel(ctx)
-	ws, err = newWatchStreamForQuery(ctx2, q)
-	if err != nil {
-		t.Fatal(err)
-	}
-	srv.addRPC(request, []interface{}{current, noChange,
-		&pb.ListenResponse{ResponseType: &pb.ListenResponse_DocumentChange{&pb.DocumentChange{
-			Document:  nil,
-			TargetIds: []int32{watchTargetID},
-		}}},
-	})
-	// Call nextSnapshot once to open the stream.
-	_, _, _, _ = ws.nextSnapshot()
-	cancel()
-	// This call to nextSnapshot will call Recv on the stream with a canceled context,
-	// so the error will come from gRPC.
-	_, _, _, err = ws.nextSnapshot()
-	codeEq(t, "cancel from Recv", codes.Canceled, err)
+	// TODO(jba): Test that we get codes.Canceled when canceling an RPC.
+	// We had a test for this in a21236af, but it was flaky for unclear reasons.
 }