tox: remove useless keyword
tox: remove useless keyword

Change-Id: Iae5d79717b25c6bdf689bd4dbaa00095214ad47f

leandroreox/gnocchi,gnocchixyz/gnocchi,leandroreox/gnocchi,sileht/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi