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)
3 jobs for flip-pitch-check-revert-1.20 in 9 minutes and 23 seconds (queued for 47 seconds)