ipatests: Remove no longer needed 'skip' compatibility
Since the required Pytest is 3.9.1+ the compat 'pytest.skip'
for Pytest < 3 can be removed.
Fixes: https://pagure.io/freeipa/issue/8101
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Sergey Orlov <sorlov@redhat.com>