lib/ccan/likely: use htable_type

lib/ccan/likely: use htable_type

Also general cleanups:
(1) Don't assume that strings are folded by the compiler.
(2) Implement likely_stats_reset().
(3) Return non-const string from likely_stats(), as caller must free it.
(4) Don't use struct info indirection (that was from when we used callbacks?)
(5) Close memory leak in run-debug.c

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
(Imported from CCAN commit 0e5d0e30b30bb07b6605843e5ff224210d8083d8)