centos: Drop c9s epel requirement for systemd-boot

It's available in the base repositories now. We still need epel on
the redhat derivatives for now.

mkosi/distributions/centos.py

@@ -101,14 +101,16 @@ def install(cls, state: MkosiState) -> None:
             if not state.config.initrds:
                 add_packages(state.config, packages, "dracut", "dracut-config-generic")
             add_packages(state.config, packages, "systemd-udev", conditional="systemd")
+            if release >= 9 and state.config.distribution == Distribution.centos:
+                add_packages(state.config, packages, "systemd-boot", conditional="systemd")
         if state.config.ssh:
             add_packages(state.config, packages, "openssh-server")
 
         if "epel" in state.config.repositories:
             add_packages(state.config, packages, "epel-release")
             if state.config.netdev:
                 add_packages(state.config, packages, "systemd-networkd", conditional="systemd")
-            if release >= 9:
+            if release >= 9 and state.config.bootable and state.config.distribution != Distribution.centos:
                 add_packages(state.config, packages, "systemd-boot", conditional="systemd")
 
         # Make sure we only install the minimal language files by default on CentOS Stream 8 which still