debian/control: remove dh-systemd build-depend

Related: OS#5223
Change-Id: I5aa41eb54ece4ff1f43079d91896747c9b85b52c
diff --git a/debian/control b/debian/control
index cf70307..2bdb50e 100644
--- a/debian/control
+++ b/debian/control
@@ -4,7 +4,6 @@
 Maintainer: Osmocom team <openbsc@lists.osmocom.org>
 Build-Depends: debhelper (>=9),
                dh-autoreconf,
-               dh-systemd (>= 1.5),
                autotools-dev,
                autoconf,
                automake,