wic: Remove dependency on rt_util module

wic: Remove dependency on rt_util module

rt_util contains bootstrap_mic(), which imports rpm and other things
we don't need because we don't do bootstrap i.e. runtime (set in
wic.conf) is always set to 'native', which means use what's on the
local host.

bootstrap mode is for downloading and installing rpms that wic needs,
which we may want to implement later; for now, we just want to use
what's local.

(From OE-Core rev: 3103f0cb908eced7b751128c2bba898d12017c80)

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>