Revisions: remove some redundant code.

* Move some slider code into the slider view that was loitering in the checkmark view.
* `this.$()`, not `$()`.
* Cache a selector.
* `toggleClass()`, not `addClass()` with a ternary.
* Remove two classes with a single `removeClass()`.

See #24425.

git-svn-id: http://core.svn.wordpress.org/trunk@24636 1a063a9b-81f0-0310-95a4-ce76da25c4cd