For #13673, put back Mac protection

Author: gplsteph

startup.py

@@ -72,7 +72,7 @@ def prepare_launch(self, exec_path, args, file_to_open=None):
         # SG TK integration for now, just run the executable with its args. This
         # allows to launch Unreal from tk-desktop or submit turntable renders
         # from Maya to Unreal, without the integration crashing Unreal.
-        if False and sys.platform == "darwin":
+        if sys.platform == "darwin":
             self.logger.warning("SG TK Unreal integration is not available on Mac.")
             return LaunchInformation(exec_path, args, required_env)