Fix broken bishop build

Summary:
* When I build the latest bishop (using buck), I get a failure and a suggestion:

```
Rule //fbobjc/Apps/Bishop:BishopPackage (//fbobjc/Apps/Bishop:BishopPlatform) FAILED because Command failed with exit code 1.

command: [/bin/bash, -e, /data/sandcastle/boxes/fbsource/buck-out/tmp/genrule-15268472800256890202.sh]

stderr: The target:  fbsource//fbobjc/Apps/Bishop:BishopShareExtension is an App Extension, and must only use APIs available in App Extensions. However, it contains dependencies that do not set 'extension_api_only = True' in their BUCK files:
 - //xplat/js/react-native-github:RCTSettingsApple

This command may be able automatically to fix this issue:
  arc buildozer 'set extension_api_only True' //xplat/js/react-native-github:RCTSettingsApple

```
* This diff is the result of running that command

Reviewed By: christophpurrer

Differential Revision: D41121880

fbshipit-source-id: b1ecd077270d7f3909739364237af32dbc617f52

BUCK

@@ -1175,6 +1175,7 @@ rn_apple_library(
         ],
     ),
     autoglob = False,
+    extension_api_only = True,
     frameworks = [
         "Foundation",
     ],