ColorBuffer: Remove the y-invert Intel GPU bug workaround

The fix in 57501158 makes sure pbuffers get initialized
properly. The previously incorrect pbuffer texture parameters
had different effects on different GPUs/drivers. On a Nvidia
GT 650M, the buffers were rendered properly but glReadPixels calls
were inverted, while Intel HD 3000/4000 seemed to get the rendering
inverted as well.

By passing proper pbuffer texture parameters, the bug (which in
itself was no driver bug but inconsistent behaviour when given
invalid parameters) vanishes.

This reverts the bug workaround parts of 9322c5cb (from
development.git).

Change-Id: Ibc38147967361cba6ba85cdf3b4e9a2e2ee6d881