Move env assignment into parseCommandLine

A bit of a misnomer but makes things more testable so I’ll accept it
until we can do more overhaul.

src/main-process/main.js

@@ -21,7 +21,6 @@ console.log = require('nslog')
 
 function start () {
   const args = parseCommandLine(process.argv.slice(1))
-  args.env = process.env
   setupAtomHome(args)
   setupCompileCache()