fix(multipathd.service): remove dependency on systemd-udev-settle

fix(multipathd.service): remove dependency on systemd-udev-settle

The dependency of multipathd on "udev settle" has recently been removed in
c9689b6 ("multipathd: Remove dependency on systemd-udev-settle.service").

But this dependency has never been necessary in the initramfs environment. It
was only required after switching root, because multipathd would potentially
tear down valid multipath maps after switching from initrd to root FS. This can
happen because dm devices "survive" the root FS switch in the udev data
base (they have the "db_persist" flag set), whereas their component devices
(SCSI etc) do not. But this can only happen after initrd-udevadm-cleanup-db.service
has been run, which happens after initrd processing.

The only dependency that's really needed is that on
systemd-udevd-kernel.socket, because multipathd depends on uevents for
devices being delivered via systemd-udevd.