Revert "Update subreddit_search to accept 'over18_state' as an argument"

This reverts commit 6261f07dc3c51a2d86a07632f70d3e70e6c97a77.
Revert "Update api.py's POST_search_reddit_names method to accept 'over18' as a param"

This reverts commit 8d3cb78069b512ceb65e54119603b2ff00849db9.
Revert "Update new link submission page's subreddit autocompletion to obey over18 state"

This reverts commit 35378ad352d57fc07c0c32dc9e493dca9920a09e.
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