Remove NOTIMPLEMENTED noise in DesktopWindowTreeHostWin

Tests pass, so it is clearly implemented enough.

BUG=339891

Review URL: https://codereview.chromium.org/141063007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249918 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249918