ipatests: Remove no longer needed 'get_marker'
'get_marker' was a compat shim for Pytest < 3.6.
Since the requred Pytest is 3.9.1+, the workaround 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>