Revert "gl: multipass renderer would use wrong source pixels sizes"

This reverts commit 9255204c264b25969558035deeae4a6d2d7f2842.

breaks HQ scaling for sw decoding on Linux

see title. A change like this should really not be hidden in a PR named vdr_fixes. Note that this is the 3rd commit of a series of elupus patches we have to revert. I would have expected a little more testing in this phase.