The test-read-alpha-texture test has been replaced with a test that
tries reading an RGBA texture in all current pixel formats. On GLES2
this should end up testing all of the convesion code because in that
case GL only supports reading back RGBA data. The test now works on
GLES2 since the conversion code for all of the formats has been added
so this also removes the GL requirement.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
