Remove SubtitlesStream#getURL()

Author: triallax

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

@@ -42,10 +42,6 @@ public String getExtension() {
         return format.suffix;
     }
 
-    public String getURL() {
-        return url;
-    }
-
     public boolean isAutoGenerated() {
         return autoGenerated;
     }