isl_map_domain: implement in terms of isl_map_project_out
isl_map_domain: implement in terms of isl_map_project_out

This makes the isl_map_domain implementation more in line
with that of isl_basic_map_domain and removes some code duplication.

Signed-off-by: Sven Verdoolaege <235c10dd23b819f81cdc9756a251746bc184cab6@gmail.com>

Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl