Fix systemd dependency

systemd is used during the build only to get systemunitdir from
systemd.pc. That pkgconfig file is now part of systemd, and
systemd-devel does not provide that, even indirectly.  While beakerlib
ends up pulling in systemd, that should not be relied upon, and does not
help for RHEL/ELN where beakerlib is now disabled.

chkconfig.spec

@@ -6,7 +6,7 @@ License: GPL-2.0-only
 URL: https://github.com/fedora-sysv/chkconfig
 Source: https://github.com/fedora-sysv/chkconfig/archive/%{version}.tar.gz#/%{name}-%{version}.tar.gz
 
-BuildRequires: gcc gettext libselinux-devel make newt-devel popt-devel systemd-devel
+BuildRequires: gcc gettext libselinux-devel make newt-devel popt-devel pkgconfig(systemd)
 # beakerlib might not be available on CentOS Stream any more
 %if 0%{?fedora}
 BuildRequires: beakerlib