systemd: do not let do_fetch depend on PACKAGECONFIG

systemd: do not let do_fetch depend on PACKAGECONFIG

It's unnecessary to make SRC_URI contains something like:
${@bb.utils.contains('PACKAGECONFIG', 'xxx', 'file://xxx', '', d)}
This does not give us any benefit and it makes do_fetch depend
on PACKAGECONFIG, which means changing of PACKAGECONFIG will result
in rerunn of do_fetch.

Besides, the related codes in do_install already does the necessary
checks.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>