core: do not filter out systemd.unit= and run-level specifier from kernel command line

Fixes a bug introduced by 846f1da465.

The commit 846f1da465 made systemd.unit=
filtered out from the command line. That causes debug-generator does not
work as expected on daemon-reexecute, and we cannot call `systemctl
daemon-reexecute` in our test suite running on nspawn.

Fixes issue reported in https://github.com/systemd/systemd/pull/23851#issuecomment-1170992052.

src/core/main.c

@@ -1721,13 +1721,6 @@ static void filter_args(
                         continue;
                 }
 
-                if (startswith(src[i],
-                               in_initrd() ? "rd.systemd.unit=" : "systemd.unit="))
-                        continue;
-
-                if (runlevel_to_target(src[i]))
-                        continue;
-
                 /* Seems we have a good old option. Let's pass it over to the new instance. */
                 dst[(*dst_index)++] = src[i];
         }