Removed autoresizing mask for modal host container view (facebook#25150)

Summary:
Fixes facebook#18177 . Related facebook#24497. Autoresizing mask would conflict with `AutoLayout`. For example , it would impact `SafeAreaView`. And actually we don't need to use autoresizing mask,  we observe the bounds change notification and [update the frame manually](https://github.com/facebook/react-native/blob/1151c096dab17e5d9a6ac05b61aacecd4305f3db/React/Views/RCTModalHostView.m#L59).

## Changelog

[iOS] [Fixed] - Removed autoresizing mask for modal host container view
Pull Request resolved: facebook#25150

Differential Revision: D15645148

Pulled By: cpojer

fbshipit-source-id: 95d5f40feaa980b959a3de6e273dccac8158c57b

Author: zhongwuzw

React/Views/RCTModalHostView.m

@@ -129,8 +129,6 @@ - (void)insertReactSubview:(UIView *)subview atIndex:(NSInteger)atIndex
     [subview addGestureRecognizer:_menuButtonGestureRecognizer];
   }
 #endif
-  subview.autoresizingMask = UIViewAutoresizingFlexibleHeight |
-                             UIViewAutoresizingFlexibleWidth;
 
   [_modalViewController.view insertSubview:subview atIndex:0];
   _reactSubview = subview;