qa/rgw: remove failing radosgw_admin_rest from multisite suite

qa/rgw: remove failing radosgw_admin_rest from multisite suite

this was added to test that admin apis forward relevent requests to the
master zone, but radosgw_admin_rest.py tries to create an admin user
with 'radosgw-admin user create'. this fails with:

Please run the command on master zone. Performing this operation on
non-master zone leads to inconsistent metadata between zones
Are you sure you want to go ahead? (requires --yes-i-really-mean-it)

Signed-off-by: Casey Bodley <cbodley@redhat.com>