chore: remove diff for [RCTDevSettings overridenKeys] (microsoft#2644)

## Summary:

This was added for an old internal use case that is no longer valid.
Let's remove it.

Author: Saadnajmi

packages/react-native/React/CoreModules/RCTDevSettings.h

@@ -30,13 +30,6 @@
  */
 - (id)settingForKey:(NSString *)key;
 
-// [macOS
-/**
- * Returns all keys that are overridden
- */
-- (NSArray<NSString *> *)overridenKeys;
-// macOS]
-
 @end
 
 @protocol RCTDevSettingsInspectable <NSObject>

packages/react-native/React/CoreModules/RCTDevSettings.mm

@@ -104,13 +104,6 @@ - (id)settingForKey:(NSString *)key
   return _settings[key];
 }
 
-// [macOS
-- (NSArray<NSString *> *)overridenKeys
-{
-  return [_settings allKeys];
-}
-// macOS]
-
 - (void)_reloadWithDefaults:(NSDictionary *)defaultValues
 {
   NSDictionary *existingSettings = [_userDefaults objectForKey:kRCTDevSettingsUserDefaultsKey];