Javadoc fixes for Bigtable client (#3652)

Author: andreamlin

google-cloud-clients/google-cloud-bigtable-admin/src/main/java/com/google/cloud/bigtable/admin/v2/BigtableInstanceAdminClient.java

@@ -926,7 +926,6 @@ public AppProfile updateAppProfile(UpdateAppProfileRequest request) {
    * ApiFuture<AppProfile> updatedAppProfileFuture = ApiFutures.transformAsync(
    *   existingAppProfileFuture,
    *   new ApiAsyncFunction<AppProfile, AppProfile>() {
-   *     @Override
    *     public ApiFuture<AppProfile> apply(AppProfile existingAppProfile) {
    *       return client.updateAppProfileAsync(
    *         UpdateAppProfileRequest.of(existingAppProfile)