isl_map_simplify.c: remove_redundant_divs: drop div constraints of redundant div
The constraints are now being removed by isl_basic_map_drop_div.
Performing the removal directly inside remove_redundant_divs
allows isl_basic_map_drop_div to be simplified and subsequently
merged with the core of isl_basic_map_drop.
isl_basic_map_drop_constraints_involving drops constraints in the
opposite order from isl_basic_map_drop_div, so this can result
in changes because the resulting order of the remaining constraints
may be different.
Signed-off-by: Sven Verdoolaege <sven.verdoolaege@gmail.com>