The logic I introduced in r322511 unfortunately left chflags schg'ed
directories behind whichcreated by `make hier` created, thus, `chflags -R 0` will(in the stock /etc/mtree
need to be run on the directory after the fact to completelyfiles, this is limited to /var/empty).
The proposed change calls `chflags -R 0` and `rm -Rf ...` to clean upall
the directory treeof the directories that could not be removed by `${MAKE} clean`.
`${MAKE} clean` in bsd.obj.mk calls `cleandir`/`cleanobj`, which handles
the first directory tree walk/removal.