Revert "reproducible-arch setup: Install multilib-devel members manually"

This reverts commit cd9e510b

.

The latest version of [core]/gcc now includes lib32 support, with an
optdepends on lkib32-gcc-libs. So installing multilib-devel should now
"Just Work".

Signed-off-by: Holger Levsen <holger@layer-acht.org>