RN: Cleanup collapsable Experiment (iOS)

Summary:
With the conclusion of D27944688 (facebook@925af8d), this backs out the experiment introduced via D27987619 (facebook@f598dd0).

Changelog:
[Internal]

Reviewed By: kacieb

Differential Revision: D28799741

fbshipit-source-id: 607ee85db26326e13dd8ddb52f5aebb732e9a354

Libraries/Components/View/ViewNativeComponent.js

@@ -13,10 +13,8 @@ import {type HostComponent} from '../../Renderer/shims/ReactNativeTypes';
 import Platform from '../../Utilities/Platform';
 import codegenNativeCommands from '../../Utilities/codegenNativeCommands';
 import ReactNativeViewViewConfigAndroid from './ReactNativeViewViewConfigAndroid';
-import ViewInjection from './ViewInjection';
 import {type ViewProps as Props} from './ViewPropTypes';
 import * as React from 'react';
-import ReactNativeViewConfigRegistry from '../../Renderer/shims/ReactNativeViewConfigRegistry';
 
 const ViewNativeComponent: HostComponent<Props> = NativeComponentRegistry.get<Props>(
   'RCTView',
@@ -26,14 +24,6 @@ const ViewNativeComponent: HostComponent<Props> = NativeComponentRegistry.get<Pr
       : {uiViewClassName: 'RCTView'},
 );
 
-if (Platform.OS === 'ios') {
-  if (ViewInjection.unstable_enableCollapsable) {
-    const viewConfig = ReactNativeViewConfigRegistry.get('RCTView');
-    // $FlowFixMe - Yes, knowingly writing to a read-only property.
-    viewConfig.validAttributes.collapsable = true;
-  }
-}
-
 interface NativeCommands {
   +hotspotUpdate: (
     viewRef: React.ElementRef<HostComponent<mixed>>,