Fix duplicate accessibilityLabels on iOS

I came across this because one of my customer's apps was freezing the UI and crashing after spending ~10 seconds when trying to read the accessibilityLabel of a view with a "particularly complex and dynamic view hierarchy". I'm still not entirely sure what the app was doing, but I believe this will sidestep the issue entirely.

I believe this change will also improve both the accessibility and the testability of RN apps, in addition to fixing that crash.

This PR supersedes or fixes facebook#21830, facebook#25963, facebook#24113, facebook#24118, appium/appium#10654, possibly facebook#25220, and probably a few other tickets I haven't identified.

Also worth mentioning that there is very similar code in https://github.com/facebook/react-native/blob/master/React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm#L489-L515 - I haven't dug into that as much, but I suspect it should probably get the same treatment. If anyone wants, I can include it in this PR.

Author: nfriedly

React/Views/RCTView.m

@@ -80,24 +80,6 @@ - (UIView *)react_findClipView
 
 @end
 
-static NSString *RCTRecursiveAccessibilityLabel(UIView *view)
-{
-  NSMutableString *str = [NSMutableString stringWithString:@""];
-  for (UIView *subview in view.subviews) {
-    NSString *label = subview.accessibilityLabel;
-    if (!label) {
-      label = RCTRecursiveAccessibilityLabel(subview);
-    }
-    if (label && label.length > 0) {
-      if (str.length > 0) {
-        [str appendString:@" "];
-      }
-      [str appendString:label];
-    }
-  }
-  return str.length == 0 ? nil : str;
-}
-
 @implementation RCTView {
   UIColor *_backgroundColor;
   NSMutableDictionary<NSString *, NSDictionary *> *accessibilityActionsNameMap;
@@ -223,7 +205,7 @@ - (NSString *)accessibilityLabel
   if (label) {
     return label;
   }
-  return RCTRecursiveAccessibilityLabel(self);
+  return nil;
 }
 
 - (NSArray<UIAccessibilityCustomAction *> *)accessibilityCustomActions