fix(45ifcfg): mark as deprecated and strictly opt-in

The `45ifcfg` module should be considered deprecated now since
ifcfg files themselves are deprecated. They've been replaced by e.g.
NetworkManager keyfiles or systemd-networkd files.

Currently, the `45ifcfg` module checks if the `/etc/sysconfig/network-
scripts` directory exists to know if to automatically get pulled in.
However, on systems with NetworkManager, this directory always exists
even if the functionality to read ifcfg files is disabled by default (NM
kindly ships a README in there to ease migrating to keyfiles).

Since almost everyone should've already migrated to a more modern
alternative, let's make this module purely opt-in now.

modules.d/45ifcfg/module-setup.sh

@@ -1,8 +1,11 @@
 #!/bin/bash
 
+# This module is deprecated. Modern replacements are NetworkManager keyfiles and
+# systemd network files. It must now be explicitly opted in by the user to be
+# added to the initrd.
+
 # called by dracut
 check() {
-    [[ -d $dracutsysrootdir/etc/sysconfig/network-scripts ]] && return 0
     return 255
 }