Re-enable Blur/Lanczos for Catalyst on OpenGL 2

Given that the Catalyst driver is now supporting direct rendering and by
that can use the OpenGL 2 code path we do no longer need to force
disable the Blur effect and Lanczos filters which used to crash in the
ARB shader path.

The ARB shader path - which can only be used in OpenGL 1 - is kept
disabled for Catalyst.

CCBUG: 270818
CCBUG: 286795
REVIEW: 106798