Get rid of @override.

- Remove superfluous @override.
- Replace @override with override
- Get rid of empty overridden method in
  `polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts`

Change-Id: Ibcf63c0d1d22e64abd36323f371549e56eee7e23
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
index 4eb33c7..a7702d1 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector.ts
@@ -48,8 +48,7 @@
 
   private readonly restApiService = appContext.restApiService;
 
-  /** @override */
-  connectedCallback() {
+  override connectedCallback() {
     super.connectedCallback();
     (
       IronA11yAnnouncer as unknown as FixIronA11yAnnouncer