mesa: simplify dispatch for glDraw* functions

mesa: simplify dispatch for glDraw* functions

Remove all the glDraw* functions from the GLvertexformat structure.
The point of that dispatch struct is to handle all the functions which
dispatch differently depending on whether we're inside glBegin/End.
glDraw* are never allowed inside glBegin/End so we can remove those
entries.

This simplifies the code paths and gets rid of quite a bit of code.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>