Removes unnecessary api-paste.ini configuration

Paremeter api_paste_config defaults to '/etc/nova/api-paste.ini',
so it is not needed to set it in nova.conf. Without having
the parameter in nova.conf we can use this module together
with dist.conf. Also filter:authtoken parameters should be
in nova.conf and not in api-paste.ini. Removes filter:authtoken
configuration from api-paste.ini in case it is filled there.

Change-Id: I85e4626076429d3e6955b7578320aac1f40d056a