Revert "timedated: support --enable-split-usr"

This reverts commit 36f9f99556.

The ntp unit information is only needed by timedated which runs in late
boot only, where all disks are around. Hence there's no point in
allowing them to be located in the rootprefix.

src/timedate/timedated.c

@@ -248,9 +248,6 @@ static char** get_ntp_services(void) {
                             "/run/systemd/ntp-units.d",
                             "/usr/local/lib/systemd/ntp-units.d",
                             "/usr/lib/systemd/ntp-units.d",
-#ifdef HAVE_SPLIT_USR
-                            "/lib/systemd/ntp-units.d",
-#endif
                             NULL);
         if (k < 0)
                 return NULL;