Clipboard addon to remove text formatting
Puretext does everything you want - and only that.
I achieve this by pasting in to Notepad (or your text-only editor of choice) and re-copying.
Works when copying from anywhere to anywhere.
But, I imagine this isn't quite what you're looking for - but it works...
As with many small tasks, AutoHotkey is perfect for the job!
^#v::
ClipboardTemp = %ClipBoardAll%
ClipBoard = %ClipBoard%
Send ^v
sleep, 30
ClipBoard = %ClipboardTemp%
Return
Would paste de-formatted text when you pressed control-win-v