Disable mentions megaphone.

app/src/main/java/org/thoughtcrime/securesms/megaphone/Megaphones.java

@@ -218,7 +218,8 @@ public final class Megaphones {
   }
 
   private static boolean shouldShowMentionsMegaphone() {
-    return FeatureFlags.mentions();
+    return false;
+//    return FeatureFlags.mentions();
   }
 
   private static boolean shouldShowLinkPreviewsMegaphone(@NonNull Context context) {