Re-implements reverse_merge! in tag model method

It looks like reverse_merge! will be available for ActionController::Parameters in 5.1:

It looks like it was merged in here: rails/rails#28355

And that pull is referenced by an issue that references the current deprecationg
warning, here: rails/rails#28353

Adding reverse_merge back makes the other_a tests pass. So it seems like the
deprecation warning can be ignored.

app/models/tag.rb

@@ -545,7 +545,6 @@ def autocomplete_score
 
   # look up tags that have been wrangled into a given fandom
   def self.autocomplete_fandom_lookup(options = {})
-    options = options.to_hash
     options.reverse_merge!({term: "", tag_type: "character", fandom: "", fallback: true})
     search_param = options[:term]
     tag_type = options[:tag_type]