Updated openstack/openstack
Project: openstack/neutron  dd6371d624dbb82110c8eb19f4c77a1592f928bf
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Cleanup HACKING.rst

* Point to new location for hacking doc
(http://docs.openstack.org/developer/hacking/)
* Remove openstack-common section because already in main hacking doc

Change-Id: I7fbcfe13469a75fed08700ccbe07fefbee33db22