RCTRootView is now has empty autoresizing mask by default

Summary: `autoresizingMask` is supposed to be set outside self class, this is UIKit convention.

Reviewed By: mmmulani

Differential Revision: D4697098

fbshipit-source-id: 7e0aa5d3032184de980b3cecafebbc4ce8ef9ada

Author: shergin

React/Base/RCTRootView.m

@@ -69,7 +69,6 @@ - (instancetype)initWithBridge:(RCTBridge *)bridge
     _loadingViewFadeDelay = 0.25;
     _loadingViewFadeDuration = 0.25;
     _sizeFlexibility = RCTRootViewSizeFlexibilityNone;
-    self.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
 
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(bridgeDidReload)