Remove GestureEventListeners

LegacyElement extends it anyway, so there is absolutely no point in
using it directly.

Change-Id: Ic91e884198d237682338db47c5037d1f844372af

polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
index 9fafcfa..f4772e3 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
@@ -14,7 +14,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import {GestureEventListeners} from '@polymer/polymer/lib/mixins/gesture-event-listeners';
 import {LegacyElementMixin} from '@polymer/polymer/lib/legacy/legacy-element-mixin';
 import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {
@@ -92,9 +91,7 @@
  *    the rest is not.
  */
 @customElement('gr-diff-processor')
-export class GrDiffProcessor extends GestureEventListeners(
-  LegacyElementMixin(PolymerElement)
-) {
+export class GrDiffProcessor extends LegacyElementMixin(PolymerElement) {
   @property({type: Number})
   context = 3;