rn: cleanup old code

This legacy code was added about a year ago to ease the migration between
releases:
631f51d627

I consider this not to be needed anymore.

react/features/calendar-sync/middleware.js

 // @flow
 
 import { SET_CONFIG } from '../base/config';
-import { ADD_KNOWN_DOMAINS, addKnownDomains } from '../base/known-domains';
+import { ADD_KNOWN_DOMAINS } from '../base/known-domains';
 import { equals, MiddlewareRegistry } from '../base/redux';
 import { APP_STATE_CHANGED } from '../mobile/background/actionTypes';
 
         case SET_CONFIG: {
             const result = next(action);
 
-            // For legacy purposes, we've allowed the deserialization of
-            // knownDomains and now we're to translate it to base/known-domains.
-            const state = store.getState()['features/calendar-sync'];
-
-            if (state) {
-                const { knownDomains } = state;
-
-                Array.isArray(knownDomains)
-                    && knownDomains.length
-                    && store.dispatch(addKnownDomains(knownDomains));
-            }
-
             _fetchCalendarEntries(store, false, false);
 
             return result;

react/features/calendar-sync/reducer.js

 // @flow
 
-import { APP_WILL_MOUNT } from '../base/app';
 import { ReducerRegistry, set } from '../base/redux';
 import { PersistenceRegistry } from '../base/storage';
 
 const STORE_NAME = 'features/calendar-sync';
 
 /**
- * NOTE 1: For legacy purposes, read any {@code knownDomains} persisted by the
- * feature calendar-sync.
- *
- * NOTE 2: Never persist the authorization value as it's needed to remain a
+ * NOTE: Never persist the authorization value as it's needed to remain a
  * runtime value to see if we need to re-request the calendar permission from
  * the user.
  */
 isCalendarEnabled()
     && PersistenceRegistry.register(STORE_NAME, {
         integrationType: true,
-        knownDomains: true,
         msAuthState: true
     });
 
 isCalendarEnabled()
     && ReducerRegistry.register(STORE_NAME, (state = DEFAULT_STATE, action) => {
         switch (action.type) {
-        case APP_WILL_MOUNT:
-            // For legacy purposes, we've allowed the deserialization of
-            // knownDomains. At this point, it should have already been
-            // translated into the new state format (namely, base/known-domains)
-            // and the app no longer needs it.
-            if (typeof state.knownDomains !== 'undefined') {
-                return set(state, 'knownDomains', undefined);
-            }
-            break;
-
         case CLEAR_CALENDAR_INTEGRATION:
             return DEFAULT_STATE;