Remove _assert_compute_node_has_enough_memory from filter_scheduler.py

Now the function _assert_compute_node_has_enough_memory has no use
in filter_scheduler.py, just remove it to make code more clean.

Change-Id: Ie6f104368140b69a60e124ea96ef6bf7715fe34e
Merge "Remove _assert_compute_node_has_enough_memory from filter_scheduler.py"