Move systemd unit to systemd folder

This folder is already in Cargo.toml (leftover from our previous units)
so let's re-use that instead of including the contrib folder that has
the specfile in it as well.

Fixes: coreos#803

Author: travier

Makefile

@@ -42,7 +42,7 @@ install-grub-static:
 	install -m 755 -d ${DESTDIR}$(PREFIX)/lib/bootupd/grub2-static/configs.d
 
 install-systemd-unit:
-	install -m 644 -D -t "${DESTDIR}$(PREFIX)/lib/systemd/system/" contrib/packaging/bootloader-update.service
+	install -m 644 -D -t "${DESTDIR}$(PREFIX)/lib/systemd/system/" systemd/bootloader-update.service
 
 bin-archive:
 	rm target/inst -rf