Allow compiler optimization (facebook#23536)

Summary:
Fixes a warning thrown by Xcode & allow RVO to be performed.

[iOS] [Fixed] - Fix Xcode warnings
Pull Request resolved: facebook#23536

Reviewed By: JoshuaGross

Differential Revision: D14142973

Pulled By: hramos

fbshipit-source-id: e23050aed811127a3b4f73aa8a74472e4cc8e98c

React/CxxBridge/RCTCxxBridge.mm

@@ -83,7 +83,7 @@ typedef NS_ENUM(NSUInteger, RCTBridgeFields) {
     bridge_.bridgeDescription =
       [NSString stringWithFormat:@"RCTCxxBridge %s",
                 ret->getDescription().c_str()];
-    return std::move(ret);
+    return ret;
   }
 
 private: