These aren't necessary any longer.

The approach of adding private headers to the build of the VLC
core doesn't work well if one wants to target multiple private
ABI versions in one build.

Instead, small shared libraries for each private ABI version
can be built separately.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 0eb7d106)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>