reproducible_freebsd.sh: Clean up obj for second build

Otherwise the second build doesn't really do much, and if even that's
not reproducible then something's gone very wrong!

This splits up some of the commands for sudo into two commands so
there's only one version of each, rather than having separate commands
for b1 and b2.

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