Fixes #1685: CPToolbar calls incorrect notification method

This fix corrects the call in CPToolbar _setWindow to `removeObserver:name:object`. Before, this was calling the non-existent `removeObserver:object`, which would raise an exception.

This was fixed by @schipmolder.
Added correct notification name.
Merge pull request #1796 from ahankinson/fix-issue1685

Fixes #1685: CPToolbar calls incorrect notification method