Move certificate exchange bits to app-connectivity

Summary: Bit of reorganising as utils is a bit too generic and crowded.

Reviewed By: passy

Differential Revision: D47186536

fbshipit-source-id: 7b1dd26db95aef00778ff4f23d91f7371c4d07ad

desktop/flipper-server-core/src/index.tsx

@@ -23,4 +23,7 @@ export {isFBBuild} from './fb-stubs/constants';
 
 export {WEBSOCKET_MAX_MESSAGE_SIZE} from './app-connectivity/ServerWebSocket';
 
-export {getAuthToken, hasAuthToken} from './utils/certificateUtils';
+export {
+  getAuthToken,
+  hasAuthToken,
+} from './app-connectivity/certificate-exchange/certificate-utils';