libvlc minor docs improvements

Minor documentation fixes:

• renaming a struct field in d3d11_player.cpp.
• removing an unecessary assignment in d3d11_player.cpp.
• aligning argument names in libvlc api definitions in libvlc_media_player.h.
• clarifying that individual struct items from the programlist are also automatically deleted in libvlc_player_programlist_delete.
• removing mention to libvlc_media_get_programlist (which does not exist).