Real fix of the fetch of the JS player at each the signatureTimestamp is required

The strings playerJsUrl, sts and playerCode are now static in order to don't fetch again the JavaScript player at each time the signatureTimestamp is needed.

Author: AudricV

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeStreamExtractor.java

@@ -93,11 +93,11 @@ public static class DeobfuscateException extends ParsingException {
     @Nullable
     private static String cachedDeobfuscationCode = null;
     @Nullable
-    private String playerJsUrl = null;
+    private static String playerJsUrl = null;
     @Nullable
-    private String sts = null;
+    private static String sts = null;
     @Nullable
-    private String playerCode = null;
+    private static String playerCode = null;
 
     @Nonnull
     private final Map<String, String> videoInfoPage = new HashMap<>();