mesa: remove unused gl_config::colorIndexMode
mesa: remove unused gl_config::colorIndexMode

Reviewed-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>
Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler