buildsystem: add 'post_unpack'

this is built-in PKG_DIR/rename replacement
hd-idle: remove 'rename' script
vdr-control: remove 'rename' script
vdr-iptv: remove 'rename' script
vdr-live: remove 'rename' script
vdr-wirbelscan: remove 'rename' script
vdr-wirbelscancontrol: remove 'rename' script