Revert [19264] to keep back-compat. Any improperly fired window.unload will...

Revert [19264] to keep back-compat. Any improperly fired window.unload will have to be dealt with on a case by case basis.

git-svn-id: https://core.svn.wordpress.org/trunk@19451 1a063a9b-81f0-0310-95a4-ce76da25c4cd