mapi_abi: Remove sanity check that all GLES functions are present.

mapi_abi: Remove sanity check that all GLES functions are present.

Currently mapi_abi.py uses hardcoded lists of function names (in
gles_api.py) to determine which functions need to be included in the
GLES 1 or GLES 2 API.  This patch removes a sanity check which
verified that all GLES functions listed in the hardcoded lists were
actually present in the XML.

Later patches in this series will modify mapi_abi.py to determine
which functions need to be included in the GLES 1 or GLES 2 API based
directly on the XML.  Once that is done, the sanity check will be
redundant.  Removing the sanity check now will simplify the patches to
come.

Tested-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>