OSX: Disable window restoration for the Mac color panel

OSX: Disable window restoration for the Mac color panel

because if it is automatically restored it's out of the application's
control, so the user's interaction will be ignored.  Change
I8ce3cd94f5ae81d7877a346743ca4e0e188baa02 did this for normal windows
by default, but the dialog helpers generate windows which aren't
affected by that.

Task-number: QTBUG-31750
Change-Id: Ida063f2d36ab038af5e85de7dfa2acf61cb6dda2
(cherry-picked from qtbase commit 69554e458669c941130c2dc03d42a59ffd00e39e)
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>