Revert "Remove libvlc_free"

As decided by the VLC TC.
 - 4 in favor: David, Denis, Hugo, Thomas
 - 1 against: Rémi

cf. discussion here https://mailman.videolan.org/pipermail/vlc-devel/2019-May/124752.html



This reverts commit fa0d7496.

Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>
Signed-off-by: David Fuhrmann <dfuhrmann@videolan.org>
Signed-off-by: Denis Charmet <typx@videolan.org>