Correct documentation libvlc_media_get_tracks_info (fix #4202)

Too many quotes.
(cherry picked from commit 5925a3846f7268fc710db8273096754b0aaf35e4)
Signed-off-by: Rémi Duraffort <ivoire@videolan.org>

include/vlc/libvlc_media.h

@@ -459,7 +459,7 @@ VLC_PUBLIC_API void *
  *
  * @begincode
  * libvlc_media_player_t *player = libvlc_media_player_new_from_media(media);
- * libvlc_media_add_option_flag(media, "sout=\"#description\"");
+ * libvlc_media_add_option_flag(media, "sout=#description");
  * libvlc_media_player_play(player);
  * // ... wait until playing
  * libvlc_media_player_release(player);