core_extensions.rb: remove unused String#to_escaped_js.

config/initializers/core_extensions.rb

@@ -12,10 +12,6 @@ module Danbooru
       def to_escaped_for_tsquery
         "'#{gsub(/\0/, '').gsub(/'/, '\0\0').gsub(/\\/, '\0\0\0\0')}'"
       end
-
-      def to_escaped_js
-        return self.gsub(/\\/, '\0\0').gsub(/['"]/) {|m| "\\#{m}"}.gsub(/\r\n|\r|\n/, '\\n')
-      end
     end
   end
 end