Outputs no cleared when converting code cell to raw

[DonJayamanne]

Switching to raw using the drop-down does not instantly make it raw and make its output disappear. It just stays here until I press Shift+Enter to execute it. I suppose one could consider this a design choice but I'd like to add my two cents that the common case for making a cell raw is that you want it out of your way for the time being. I infact use raw cells half the time to just clear the output in a way.

Originally filed here #16122