Remove overriden field `url`

extractor/src/main/java/org/schabi/newpipe/extractor/stream/SubtitlesStream.java

@@ -8,7 +8,6 @@ import java.util.Locale;
 public class SubtitlesStream extends Stream implements Serializable {
     private final MediaFormat format;
     private final Locale locale;
-    private final String url;
     private final boolean autoGenerated;
     private final String code;
 
@@ -34,7 +33,6 @@ public class SubtitlesStream extends Stream implements Serializable {
         }
         this.code = languageCode;
         this.format = format;
-        this.url = url;
         this.autoGenerated = autoGenerated;
     }