mplayer2: cleanup empty directories

The mplayer "make install" phase leaves an empty
/usr/lib directory seemingly regardless of the setting
of libdir.  Remove it to avoid a packaging warning.

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>
Signed-off-by: Awais Belal <awais_belal@mentor.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>