Bug 1440207 - Part 1: Stop setting `gArgc` and `gArgv` in content, r=ipc-reviewers,mccr8

It is never used outside of the parent process.

Differential Revision: https://phabricator.services.mozilla.com/D221369

toolkit/xre/nsEmbedFunctions.cpp

@@ -394,9 +394,6 @@ nsresult XRE_InitChildProcess(int aArgc, char* aArgv[],
     }
   }
 
-  gArgv = aArgv;
-  gArgc = aArgc;
-
 #ifdef MOZ_X11
   XInitThreads();
 #endif