reactions: Remove the touch feedback of "Cancel" button in emoji picker

Before this change, the Cancel button showed a faint background
highlight when pressed, that extended horizontally to touch both the
emoji search input and the screen edge, which looked odd.

Removing the touch feedback also aligns it with Cancel and Compose
buttons in the new-dm sheet.

Author: sm-sayedi

lib/widgets/emoji_reaction.dart

@@ -554,10 +554,8 @@ class _EmojiPickerState extends State<EmojiPicker> with PerAccountStoreAwareStat
               padding: const EdgeInsets.symmetric(horizontal: 8),
               splashFactory: NoSplash.splashFactory,
               foregroundColor: designVariables.contextMenuItemText,
-            ).copyWith(backgroundColor: WidgetStateColor.resolveWith((states) =>
-              states.contains(WidgetState.pressed)
-                ? designVariables.contextMenuItemBg.withFadedAlpha(0.20)
-                : Colors.transparent)),
+              overlayColor: Colors.transparent,
+            ),
             child: Text(zulipLocalizations.dialogCancel,
               style: const TextStyle(fontSize: 20, height: 30 / 20))),
         ])),