include: remove host command tests from host.mk

Those tests are part of prereq-build.mk now.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44273 3c298f89-4303-0410-b956-a3cf2f4a3e73