Remove duplicated option state_path from netns cleanup

state_path is already declared in quantum/common/config.py,
so we need to remove state_path option from netns_cleanup_util.

Fixes bug 1122822

Change-Id: Ifc1c0290c00c1fe5e2fc1833144da05615a782ef
Merge "Remove duplicated option state_path from netns cleanup"