For |make firefox/mozcentral| builds, add cleanupJSSource to remove duplicate file headers in extensions/firefox/content/PdfjsChromeUtils.jsm
Merge pull request #5312 from Snuffleupagus/e10s-fixes-2

For |make firefox/mozcentral| builds, add cleanupJSSource to remove duplicate file headers in extensions/firefox/content/PdfjsChromeUtils.jsm