Remove unused methods

Remove unused methods

 o cinder/volume/driver.py
   - def _get_iscsi_initiator(self):

     This method was removed in the following commit.

       commit cb6faab4d99801e76195802659013a5ccdc6b5b5
       Author: Walter A. Boring IV <walter.boring@hp.com>
       Date:   Wed Jul 10 15:22:06 2013 -0700

           Add Brick Fibre Channel attach/detach support.

 o cinder/volume/utils.py
   - def get_host_from_queue(queuename):

     This method was added in the following commit.

       commit 6c708d12f58eb20fce6733f1f6fd08d978570775
       Author: Michael Basnight <mbasnight@gmail.com>
       Date:   Mon Feb 11 15:54:45 2013 -0600

           Update cinder-volume to enable multi volume support

     But there is no evidence that was used.

   - def notify_usage_exists(context, volume_ref, current_period=False):

     This method was removed in the following commit.

       commit d09b7c78b3c905badb1112434eb9c09c2c8ffb5a
       Author: Ollie Leahy <oliver.leahy@hp.com>
       Date:   Thu Dec 12 11:01:34 2013 +0000

           Allow user to specify audit period.

Change-Id: I819679e03df9a2a848004d14e3f55821c88834a4