sources: replace HTTParty with Danbooru::Http in http_exists?.

app/logical/sources/strategies/art_station.rb

@@ -147,7 +147,7 @@ module Sources::Strategies
         urls = urls.reverse
       end
 
-      chosen_url = urls.find { |url| http_exists?(url, headers) }
+      chosen_url = urls.find { |url| http_exists?(url) }
       chosen_url || url
     end
   end

app/logical/sources/strategies/base.rb

@@ -288,9 +288,8 @@ module Sources
         to_h.to_json
       end
 
-      def http_exists?(url, headers)
-        res = HTTParty.head(url, Danbooru.config.httparty_options.deep_merge(headers: headers))
-        res.success?
+      def http_exists?(url, headers = {})
+        http.headers(headers).head(url).status.success?
       end
 
       # Convert commentary to dtext by stripping html tags. Sites can override

app/logical/sources/strategies/tumblr.rb

@@ -168,7 +168,7 @@ module Sources::Strategies
       end
 
       candidates.find do |candidate|
-        http_exists?(candidate, headers)
+        http_exists?(candidate)
       end
     end