zIndex prop was removed from RCTShadowView

Summary:
This was leftovers from old implementation of zIndex feature.
Janic janicduplessis refactored this and moved all logic to UIView layer, so we don't need this prop anymore in shadow realm.
More info: #14011

Reviewed By: mmmulani

Differential Revision: D6574414

fbshipit-source-id: 2cae19350765689784d7884ed875878d39b4e3f1

React/Views/RCTShadowView.h

@@ -170,11 +170,6 @@ typedef void (^RCTApplierBlock)(NSDictionary<NSNumber *, UIView *> *viewRegistry
 
 @property (nonatomic, assign) float aspectRatio;
 
-/**
- * z-index, used to override sibling order in the view
- */
-@property (nonatomic, assign) NSInteger zIndex;
-
 /**
  * Interface direction (LTR or RTL)
  */

React/Views/RCTShadowView.m

@@ -792,16 +792,6 @@ - (void)setBackgroundColor:(UIColor *)color
   [self dirtyPropagation];
 }
 
-- (void)setZIndex:(NSInteger)zIndex
-{
-  _zIndex = zIndex;
-  if (_superview) {
-    // Changing zIndex means the subview order of the parent needs updating
-    _superview->_didUpdateSubviews = YES;
-    [_superview dirtyPropagation];
-  }
-}
-
 - (void)didUpdateReactSubviews
 {
   // Does nothing by default

React/Views/RCTViewManager.m

@@ -336,7 +336,6 @@ - (RCTViewManagerUIBlock)uiBlockToAmendWithShadowViewRegistry:(__unused NSDictio
 
 RCT_EXPORT_SHADOW_PROPERTY(onLayout, RCTDirectEventBlock)
 
-RCT_EXPORT_SHADOW_PROPERTY(zIndex, NSInteger)
 RCT_EXPORT_SHADOW_PROPERTY(direction, YGDirection)
 
 @end