Revert "present/scmd: Check that the flip and screen pixmap pitches match"
This reverts commit ef91da27.
I thought this couldn't work under any circumstances, but I was wrong,
and drivers are already checking for cases that really cannot work.
Fixes issue #839.
(cherry picked from commit 2f0dd181)
9 minutes and 23 seconds
(queued for 47 seconds)