Use yargs for non-headless Flipper args parsing

Summary:
This seems like a better approach than ad-hoc lookup in
`electron.remove.argv`. Left a note to a task to provide
a better interface to this.

I also need this in order to ensure we're starting
Flipper through the launcher which needs to happen
before we start the Electron runtime.

Reviewed By: jknoxville

Differential Revision: D13881355

fbshipit-source-id: 69c70d71035a47084f789ddb4dc969b45ba4648b

headless/index.js

@@ -47,7 +47,7 @@ yargs
     startFlipper,
   )
   .version(global.__VERSION__)
-  .help().argv;
+  .help();
 
 function startFlipper({
   dev,