mesa: rgb10_a2 is never color-renderable in gles2
Fixes dEQP-GLES2.functional.fbo.completeness.renderable.texture.color0.rgb10_a2 on GLES2 drivers which support RGB10_A2 textures. GL_OES_required_internalformat does not make it a color-renderable format.
Closes: #4972 (closed) Signed-off-by: Ilia Mirkin imirkin@alum.mit.edu