xbmk: remove xbloc, re-use xbtmp instead

we no longer separate them. xbloc was the on-disk
tmp directory, whereas xbtmp used to be in /tmp
which we assumed to be tmpfs (it may not be, but
often is on many workstation setups - and our
documentation recommended doing this).

as mentioned in the previous commit, benchmarking
shows little speed difference using tmpfs /tmp
versus on-disk /tmp, for our purposes at least.
therefore, the handling of tmp files is being
greatly simplified.

Signed-off-by: Leah Rowe <leah@libreboot.org>

mk

@@ -37,5 +37,6 @@ main "$@" && exit 0
 . "include/tree.sh"
 
 trees "$@" || exit 0
+x_ touch "$mkhelpercfg"
 . "$mkhelpercfg"
 $cmd