libvlc: media_discoverer: remove mention to event_manager

The libvlc_media_discoverer_event_manager has been deprecated since
518cbead.

Signed-off-by: Alexandre Janniaux <ajanni@videolabs.io>

include/vlc/libvlc_media_discoverer.h

@@ -78,7 +78,6 @@ typedef struct libvlc_media_discoverer_t libvlc_media_discoverer_t;
  * discovery.
  *
  * \see libvlc_media_discoverer_media_list
- * \see libvlc_media_discoverer_event_manager
  * \see libvlc_media_discoverer_start
  *
  * \param p_inst libvlc instance