uploads: don't autotag sound on videos.

Don't automatically add the sound tag to videos. This was incorrect
nearly 20% of the time because of silent audio tracks. This error rate
is too high.

https://danbooru.donmai.us/posts?tags=exif:Track2:AudioChannels+-sound
https://danbooru.donmai.us/posts?tags=exif:Track1:AudioChannels+-sound

app/logical/upload_service/utils.rb

@@ -17,17 +17,10 @@ class UploadService
       upload.image_height = media_file.height
 
       upload.validate!(:file)
-      upload.tag_string = "#{upload.tag_string} #{Utils.automatic_tags(media_file)}"
 
       MediaAsset.upload!(media_file)
     end
 
-    def automatic_tags(media_file)
-      tags = []
-      tags << "sound" if media_file.has_audio?
-      tags.join(" ")
-    end
-
     def get_file_for_upload(source_url, referer_url, file)
       return MediaFile.open(file) if file.present?
       raise "No file or source URL provided" if source_url.blank?