TmpFS inodes rely on the call to Inode::one_ref_left() to unregister
themselves from the inode cache in TmpFS.
When moving various kernel classes to ListedRefCounted for safe unref()
while participating on lists, I forgot to make ListedRefCounted check
for (and call) one_ref_left() & will_be_destroyed() on the CRTP class.
This class implements the emerging "ref-counted object that participates
in a lock-protected list that requires safe removal on unref()" pattern
as a base class that can be inherited in place of RefCounted<T>.
