Media: Reset modal after gallery insertion.

Removes hardcoded (and vestigial) 'upload' states in favor of using the default modal state.
When a media toolbar action is triggered, reset the modal after switching to the new state (as opposed to beforehand).

fixes #23675.


git-svn-id: https://core.svn.wordpress.org/trunk@23590 1a063a9b-81f0-0310-95a4-ce76da25c4cd