Avoid systemd_requires as per updated packaging guidelines

There is no need to have them as systemd correctly handles reloading
depending on the transaction ordering (even if systemd is installed
_after_ the package that installs the unit file).

Additionally, this also drops hard requires on /usr/bin/systemctl and
just makes the scriptlets that call systemctl conditional on systemctl
being present.

All of this helps avoid pulling in full systemd for container setups.

dbus-broker.spec

@@ -2,13 +2,12 @@
 
 Name:                 dbus-broker
 Version:              29
-Release:              3%{?dist}
+Release:              4%{?dist}
 Summary:              Linux D-Bus Message Broker
 License:              ASL 2.0
 URL:                  https://github.com/bus1/dbus-broker
 Source0:              https://github.com/bus1/dbus-broker/releases/download/v%{version}/dbus-broker-%{version}.tar.xz
 Patch0000:            28af5ac996c94922fc49660e0efa955f57575187.patch
-%{?systemd_requires}
 BuildRequires:        pkgconfig(audit)
 BuildRequires:        pkgconfig(expat)
 BuildRequires:        pkgconfig(dbus-1)
@@ -22,9 +21,6 @@ BuildRequires:        meson
 BuildRequires:        python3-docutils
 Requires:             dbus-common
 Requires(pre):        shadow-utils
-Requires(post):       /usr/bin/systemctl
-# for triggerpostun
-Requires:             /usr/bin/systemctl
 
 %description
 dbus-broker is an implementation of a message bus as defined by the D-Bus
@@ -72,7 +68,7 @@ exit 0
 %systemd_user_postun dbus-broker.service
 
 %triggerpostun -- dbus-daemon
-if [ $2 -eq 0 ] ; then
+if [ $2 -eq 0 ] && [ -x /usr/bin/systemctl ] ; then
         # The `dbus-daemon` package used to provide the default D-Bus
         # implementation. We continue to make sure that if you uninstall it, we
         # re-evaluate whether to enable dbus-broker to replace it. If we didnt,
@@ -94,6 +90,9 @@ fi
 %{_userunitdir}/dbus-broker.service
 
 %changelog
+* Fri Oct 01 2021 Kalev Lember <klember@redhat.com> - 29-4
+- Avoid systemd_requires as per updated packaging guidelines
+
 * Thu Jul 29 2021 Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> - 29-3
 - Drop the ordering on sysinit.target (#1976653)