debrepo-update-sub: disable signing packages

Signing the packages increases their size.
	When the client (for whatever reason) needs to get a
	package X from another repo (REPO B) instead of ours
	(REPO A), X's size is taken from A's lists, which
	includes the signature at the end. The client downloads
	X from A, but it is smaller than it should be (A's version
	of X) and stops.