This reverts commit 288fa407.

The only reason old pixman versions didn't work was the missing
PIXMAN_TYPE_BGRA, which is properly #ifdef'ed now.  So we don't
have to require a minimum pixman version.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>