talloc: use TC_UNDEFINE_SHRINK_CHUNK() instead of TC_INVALIDATE_SHRINK_CHUNK() for...

talloc: use TC_UNDEFINE_SHRINK_CHUNK() instead of TC_INVALIDATE_SHRINK_CHUNK() for realloc path

If we optimize on top of raw realloc() we need
TC_INVALIDATE_SHRINK_CHUNK together with TC_UNDEFINE_GROW_CHUNK
(with was missing and caused false positive valgrind warnings).

But that is really slow, as we do a lot of talloc_realloc calls in samba.

That's why we only to TC_UNDEFINE_SHRINK_CHUNK() for now.

metze