[RN] Fix redux state cleanup

The preceding commit "fix(auth.native): trigger conference left on
cancel" did not correctly clean the redux state up on CONFERENCE_LEFT.

react/features/authentication/actions.js

 export function cancelWaitForOwner() {
     return (dispatch: Dispatch<*>, getState: Function) => {
         dispatch(stopWaitForOwner());
+
+        // XXX The error associated with CONFERENCE_FAILED was marked as
+        // recoverable by the feature room-lock and, consequently,
+        // recoverable-aware features such as mobile's external-api did not
+        // deliver the CONFERENCE_FAILED to the SDK clients/consumers. Since the
+        // app/user is going to nativate to WelcomePage, the SDK
+        // clients/consumers need an event.
         const { authRequired } = getState()['features/base/conference'];
 
-        if (authRequired) {
-            dispatch(conferenceLeft(authRequired));
-        }
+        authRequired && dispatch(conferenceLeft(authRequired));
 
         dispatch(appNavigate(undefined));
     };

react/features/base/conference/reducer.js

  * reduction of the specified action.
  */
 function _conferenceLeft(state, { conference }) {
-    let output = state;
+    let nextState = state;
 
     if (state.authRequired === conference) {
-        output = set(output, 'authRequired', undefined);
+        nextState = set(nextState, 'authRequired', undefined);
     }
     if (state.conference === conference) {
-        output = assign(output, {
+        nextState = assign(nextState, {
             conference: undefined,
             joining: undefined,
-            leaving: undefined
+            leaving: undefined,
+
+            // XXX Clear/unset locked & password here for a conference which has
+            // been LOCKED_LOCALLY.
+            locked: undefined,
+            password: undefined
         });
     }
     if (state.passwordRequired === conference) {
-        // Note that in case the conference was joined those fields have been
-        // cleared already, so this step needs to be done only if the room
-        // unlock operation has been canceled and that's why it's not done in
-        // the 'state.conference' condition above.
-        output = assign(output, {
+        nextState = assign(nextState, {
+            // XXX Clear/unset locked & password here for a conference which has
+            // been LOCKED_REMOTELY.
             locked: undefined,
             password: undefined,
             passwordRequired: undefined
         });
     }
 
-    return output;
+    return nextState;
 }
 
 /**