Revert "Update subreddit_search to accept 'include_over18' as an argument"

This reverts commit 537e564221dcd79b94392c91b486748ff06175d7.
Revert "Update api.py's POST_search_reddit_names method to accept 'over_18' as a param"

This reverts commit fa883fa58fd33ca3e69d59da8733ec97ab74ec1e.
Revert "Update new link submission page's subreddit autocompletion to obey over18 state"

This reverts commit 4e149247a24ddaddb80883fd8a57451c43757c04.
Update subreddit_search to accept 'include_over18' as an argument
Update api.py's POST_search_reddit_names method to accept 'over_18' as a param
Update new link submission page's subreddit autocompletion to obey over18 state