We hard code configure options in tox.ini to generate Magnum config
sample file, and we keep this config sample file in our repository
before.
It is inconvenient for developer if the add/remove/change some
configuration options cause they need to take care about the
config.sample file.
This patch removes magnum.config.sample instead of letting admin generate it
from magnum-config-generator.conf(picked from tox.ini).
P.S. Make tox.ini cleanup since it is not a good idea we mess up tox.ini
with configuration options.
Closes-Bug: #1538374
Change-Id: I80d019b5c98e0282cd0fe50fd4ad66286287e2cb
022bba9c06