Remove only_free param to Pool.get()
Remove only_free param to Pool.get()

This is unused. I think I added it before iter_free(), i.e. empty()
was going to be:

  for item in self.get(only_free=True):
      item.close()

rather than:

  for item in self.iter_free():
      item.close()

Change-Id: Ie6d0de3b7453ee036412db10f37d26f04de73cf7

stevei101/oslo.messaging,redhat-openstack/oslo.messaging,apporc/oslo.messaging,dims/oslo.messaging,isyippee/oslo.messaging,ozamiatin/oslo.messaging,redhat-openstack/oslo.messaging,magic0704/oslo.messaging,ozamiatin/oslo.messaging,JioCloud/oslo.messaging,hkumarmk/oslo.messaging,zhurongze/oslo.messaging,stevei101/oslo.messaging,hkumarmk/oslo.messaging,dukhlov/oslo.messaging,viggates/oslo.messaging,apporc/oslo.messaging,magic0704/oslo.messaging,isyippee/oslo.messaging,citrix-openstack-build/oslo.messaging,dims/oslo.messaging,eayunstack/oslo.messaging,dukhlov/oslo.messaging,zhurongze/oslo.messaging