[downloader:ytdl] change 'forward-cookies' default to 'false'

There are currently no situations where forwarding gallery-dl's cookies
to youtube-dl is necessary, and it only causes problems when forcing
youtube-dl for Twitter video downloads while logged in.

docs/configuration.rst

@@ -1402,7 +1402,7 @@ downloader.ytdl.forward-cookies
 -------------------------------
 =========== =====
 Type        ``bool``
-Default     ``true``
+Default     ``false``
 Description Forward cookies to youtube-dl.
 =========== =====
 

docs/gallery-dl.conf

@@ -196,7 +196,7 @@
         "ytdl":
         {
             "format": null,
-            "forward-cookies": true,
+            "forward-cookies": false,
             "mtime": true,
             "outtmpl": null,
             "rate": null,