Demolishing of background color propagation infra

Summary: As it was mentioned in previous diffs, we are removing this because it overcomplicates rendering layer and provides (almost) no benefits (and cannot be implemented 100% accurate way).

Reviewed By: mmmulani

Differential Revision: D6582560

fbshipit-source-id: 0778db96a45dd8e2520268d5d00792677cb01a20

React/Base/RCTRootContentView.m

@@ -18,9 +18,6 @@
 #import "UIView+React.h"
 
 @implementation RCTRootContentView
-{
-  UIColor *_backgroundColor;
-}
 
 - (instancetype)initWithFrame:(CGRect)frame
                        bridge:(RCTBridge *)bridge
@@ -34,7 +31,6 @@
     _touchHandler = [[RCTTouchHandler alloc] initWithBridge:_bridge];
     [_touchHandler attachToView:self];
     [_bridge.uiManager registerRootView:self];
-    self.layer.backgroundColor = NULL;
   }
   return self;
 }
@@ -89,19 +85,6 @@ RCT_NOT_IMPLEMENTED(-(instancetype)initWithCoder:(nonnull NSCoder *)aDecoder)
   [_bridge.uiManager setAvailableSize:self.availableSize forRootView:self];
 }
 
-- (void)setBackgroundColor:(UIColor *)backgroundColor
-{
-  _backgroundColor = backgroundColor;
-  if (self.reactTag && _bridge.isValid) {
-    [_bridge.uiManager setBackgroundColor:backgroundColor forView:self];
-  }
-}
-
-- (UIColor *)backgroundColor
-{
-  return _backgroundColor;
-}
-
 - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
 {
   // The root content view itself should never receive touches