Revert [28963].

see #28006.
Built from https://develop.svn.wordpress.org/trunk@29235


git-svn-id: http://core.svn.wordpress.org/trunk@29019 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE wpView:
- Typing something replaces a selected view.
- Pressing backspace deletes the selection.
- Pressing enter also deletes the selection.
- Pasting something replaces the selection.
- Also merge the different 'keydown' handlers.
Props avryl, fixes #28913.
Built from https://develop.svn.wordpress.org/trunk@29236


git-svn-id: http://core.svn.wordpress.org/trunk@29020 1a063a9b-81f0-0310-95a4-ce76da25c4cd