pixman: avoid unnecessary y-flip for screen capture
Commit 4fc5dd00 ("compositor: add capability CAPTURE_YFLIP") introduced a capability flag which indicates whether y-flipping is necessary. As already indicated in that commit message, it seems that pixman flipps the y-axis only due to historic reasons.
Drop y-flipping and use the WESTON_CAP_CAPTURE_YFLIP flag to indicate that y-flipping is not necessary. This simplifies code and improves screen share performance (on my test by about 3% down to 18% CPU load on the sharing instance of Weston).
Signed-off-by: Stefan Agner firstname.lastname@example.org