lib: clean/restore memory debugging functions

lib: clean/restore memory debugging functions

This adapts the dump-at-exit handler and removes the old leftover code.

(Note the text in log_memtype_stderr was actually incorrect as the only
caller in bgpd cleans up configuration before calling it, i.e. any
remaining allocations are missing-cleanup bugs.)

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
Acked-by: Vincent JARDIN <vincent.jardin@6wind.com>
Acked-by: Donald Sharp <sharpd@cumulusnetworks.com>