cleanup tox.ini
cleanup tox.ini

* Remove skipsdist : Needs to be set only if 
  sdist is expensive
* Remove usedevelop : only needed when skipsdist 
  is set to True
* Remove install_command : We can just use the 
  default, we don't need to override
* Remove setenv : We can just use the default as
  we don't need any extra environment variables
* Remove requirements.txt from deps, as this is
  already added automatically

Change-Id: I334c8db354f212f3f990f3ba59f2aa46355dae74
openstack/oslo.service