BuildSystem: Automatically delete libtool files

Half of the ports had a manual post_install step to delete libtool files
this is now done automatically and there is no need for it!

Libtool files have to be deleted as libtool doesn't work while
cross-compiling (at least out of the box)

ports/libffi/build.sh

@@ -4,8 +4,3 @@ NAME='libffi'
 VERSION='3.5.2'
 DOWNLOAD_URL="https://github.com/libffi/libffi/releases/download/v$VERSION/libffi-$VERSION.tar.gz#f3a3082a23b37c293a4fcd1053147b371f2ff91fa7ea1b2a52e335676bac82dc"
 CONFIG_SUB=('config.sub')
-
-post_install() {
-	# remove libtool file
-	rm -f $BANAN_SYSROOT/usr/lib/libffi.la
-}