Bug 990762 Remove deprecation in content scripts for global 'postWorker'
so that the native 'window.postWorker' can communicate to other windows.
Remove tests for postMessge wrapper proxy (fails due to global proxy
that is a separate concern in bug 996208)
Merge pull request #1457 from jsantell/990762-window-postmessage-in-cscripts

Bug 990762 Remove deprecation in content scripts for global 'postWorker'... r=@ZER0