lib: fix a segfault introduced in ef3707 when freeing an atom

lib: fix a segfault introduced in ef3707 when freeing an atom

In the change "lldpd: make notifications work when a port goes down",
a regression was introduced. It is important to never call
`TAILQ_REMOVE` on a marshalled struct, like when we are in
liblldpctl. This is because the marshalling process does not keep a
real list (prev pointer is incorrect).

The change ef3707 did introduce a regression by calling TAILQ_REMOVE
in a case where it is useless. We only need to call TAILQ_REMOVE if we
won't empty the whole list. So when we call `lldpd_remote_cleanup()`
with `all` set to `1`, we don't need to call TAILQ_REMOVE.