artists: clean up artist finding logic.

Rename Artist#find_all_by_url to url_matches and drop previous
url_matches method, along with find_artists and search_for_profile.

Previously find_artists tried to lookup the url, referer url, and profile
url in turn until an artist match was found. This was wasteful, because
the source strategy already knows which url to lookup (usually the profile
url). If that url doesn't find a match, then the artist doesn't exist.

app/models/artist.rb

@@ -148,7 +148,7 @@ class Artist < ApplicationRecord
         %r!\Ahttps?://(?:[a-zA-Z0-9_-]+\.)*#{domain}/\z!i
       end)
 
-      def find_all_by_url(url)
+      def url_matches(url)
         url = ArtistUrl.normalize(url)
         artists = []
 
@@ -163,7 +163,7 @@ class Artist < ApplicationRecord
           break if url =~ SITE_BLACKLIST_REGEXP
         end
 
-        artists.inject({}) {|h, x| h[x.name] = x; h}.values.slice(0, 20)
+        where(id: artists.uniq(&:name).take(20))
       end
     end
 
@@ -456,40 +456,6 @@ class Artist < ApplicationRecord
   end
 
   module SearchMethods
-    def find_artists(url, referer_url = nil)
-      artists = url_matches(url).order("id desc").limit(10)
-
-      if artists.empty? && referer_url.present? && referer_url != url
-        artists = url_matches(referer_url).order("id desc").limit(20)
-      end
-
-      artists
-    rescue PixivApiClient::Error => e
-      []
-    end
-
-    def url_matches(string)
-      matches = find_all_by_url(string).map(&:id)
-
-      if matches.any?
-        where("id in (?)", matches)
-      elsif matches = search_for_profile(string)
-        where("id in (?)", matches)
-      else
-        where("false")
-      end
-    end
-
-    def search_for_profile(url)
-      source = Sources::Strategies.find(url)
-      find_all_by_url(source.profile_url)
-    rescue Net::OpenTimeout, PixivApiClient::Error
-      raise if Rails.env.test?
-      nil
-    rescue Exception
-      nil
-    end
-
     def other_names_match(string)
       if string =~ /\*/ && CurrentUser.is_builder?
         where("artists.other_names ILIKE ? ESCAPE E'\\\\'", string.to_escaped_for_sql_like)