Remove the ATI_envmap_bumpmap extension

Remove the ATI_envmap_bumpmap extension

As far as I can tell, the Intel mesa driver is the only driver in the world
still supporting this legacy extension.  If someone wants to do bump
mapping, they can use shaders.

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> [v1]
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz> [v2]
Reviewed-by: Ian Romanick <idr@freedesktop.org> [v3]