meta: clear_state structure cleanup

meta: clear_state structure cleanup

Remove unused variables from clear_state and use a hardcoded location
for color uniform to get rid of 2 more variables. Modify shaders to use
explicit location for vertex attribute too as extension is enabled.

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>