Revert "package/pkg-autotools.mk: fix runtime path"

This reverts commit c28b2703.

This still broke packages using certain older autoconf versions (E.G.  2.13
as used by thttpd/wipe).

Acked-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>