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>

src/mapi/glapi/gen/gl_genexec.py

@@ -32,10 +32,7 @@ import sys, getopt
 
 
 exec_flavor_map = {
-    'check': '_check_',
     'dynamic': None,
-    'es': '_es_',
-    'loopback': 'loopback_',
     'mesa': '_mesa_',
     'skip': None,
     }