Unliking a post updates like count on front end (#12140)

* return the new favourites_count
when unfavouriting a status

* Remove trailing whitespace

* revert changes to favourites_controller

* Decrease favourites_count through statuses reducer

* styling fix

* Fix missing trailing comma

app/javascript/mastodon/reducers/statuses.js

@@ -3,6 +3,7 @@ import {
   REBLOG_FAIL,
   FAVOURITE_REQUEST,
   FAVOURITE_FAIL,
+  UNFAVOURITE_SUCCESS,
 } from '../actions/interactions';
 import {
   STATUS_MUTE_SUCCESS,
@@ -37,6 +38,9 @@ export default function statuses(state = initialState, action) {
     return importStatuses(state, action.statuses);
   case FAVOURITE_REQUEST:
     return state.setIn([action.status.get('id'), 'favourited'], true);
+  case UNFAVOURITE_SUCCESS:
+    const favouritesCount = action.status.get('favourites_count');
+    return state.setIn([action.status.get('id'), 'favourites_count'], favouritesCount - 1);
   case FAVOURITE_FAIL:
     return state.get(action.status.get('id')) === undefined ? state : state.setIn([action.status.get('id'), 'favourited'], false);
   case REBLOG_REQUEST: