glapi: Stop handling XML annotation exec="{es,check,loopback}".

glapi: Stop handling XML annotation exec="{es,check,loopback}".

Previously, we used these XML annotations to make the code generation
scripts aware of any instances where the Mesa implementation of a
function had a prefix other than "_mesa_".  Now that all of the mesa
implementation functions have been renamed to match the XML, we only
need to handle exec="skip", exec="dynamic", and the default case of
exec="mesa".

Acked-by: Brian Paul <brianp@vmware.com>