Removed note about defining new site's default ask group via
settings.ASKBOT_SITE_TO_DEFAULT_ASK_GROUP because this is no longer used
by the code. It's been deprecated in favour of per-site
settings.DEFAULT_ASK_GROUP_ID.
Merge pull request #337 from knowledgepoint-devs/merge1

settings.ASKBOT_SITE_TO_DEFAULT_ASK_GROUP no longer used