spec: drop/update dependencies on systemd-{units,sysv}

-sysv was probably a left-over, and the -units deps was outdated and not
necessary, see
https://docs.fedoraproject.org/en-US/packaging-guidelines/Scriptlets/#_dependencies_on_the_systemd_package.

Only for 'systemctl mask' which is executed in %post, we want to make
sure that /usr/bin/systemctl is installed, so keep that dependency.
(A file dep is used to avoid issues if the systemd package is further
split later on.)

Ferried over from https://src.fedoraproject.org/rpms/libvirt/pull-request/7.

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>

libvirt.spec.in

@@ -247,7 +247,6 @@ BuildRequires: ninja-build
 BuildRequires: git
 BuildRequires: perl-interpreter
 BuildRequires: python3
-BuildRequires: systemd-units
 %if %{with_libxl}
 BuildRequires: xen-devel
 %endif
@@ -412,10 +411,7 @@ Requires: polkit >= 0.112
 Requires: dmidecode
 %endif
 # For service management
-Requires(post): systemd-units
-Requires(post): systemd-sysv
-Requires(preun): systemd-units
-Requires(postun): systemd-units
+Requires(post): /usr/bin/systemctl
 %if %{with_numad}
 Requires: numad
 %endif