Remove _extract_roles method from neutron.policy
Remove _extract_roles method from neutron.policy

This method is not used anymore as it was called only from
the get_admin_roles method. This method has been removed
by commit 734e77365b0f241a3cea0f3c9dfb1d5fcf6eac8c; therefore
the _extract_roles method is now zombie code and should be
removed before it starts feeding on Neutron's brain.

Related-Bug: #1445690

Change-Id: I0306bcea813031897e319af9693e18d03848e378

cloudbase/neutron,klmitch/neutron,huntxu/neutron,igor-toga/local-snat,noironetworks/neutron,SamYaple/neutron,apporc/neutron,huntxu/neutron,klmitch/neutron,yanheven/neutron,chitr/neutron,noironetworks/neutron,jumpojoy/neutron,glove747/liberty-neutron,wolverineav/neutron,openstack/neutron,apporc/neutron,igor-toga/local-snat,dims/neutron,bigswitch/neutron,eayunstack/neutron,eayunstack/neutron,dims/neutron,SamYaple/neutron,dhanunjaya/neutron,openstack/neutron,swdream/neutron,sebrandon1/neutron,swdream/neutron,asgard-lab/neutron,asgard-lab/neutron,MaximNevrov/neutron,openstack/neutron,yanheven/neutron,dhanunjaya/neutron,mahak/neutron,wolverineav/neutron,jumpojoy/neutron,glove747/liberty-neutron,bigswitch/neutron,sebrandon1/neutron,cloudbase/neutron,mahak/neutron,MaximNevrov/neutron,chitr/neutron,mahak/neutron