Remove tal_len, use tal_count() or tal_bytelen().

tal_count() is used where there's a type, even if it's char or u8, and
tal_bytelen() is going to replace tal_len() for clarity: it's only needed
where a pointer is void.

We shim tal_bytelen() for now.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/memleak.c

@@ -128,7 +128,7 @@ static void scan_for_pointers(struct htable *memtable, const tal_t *p)
 	size_t i, n;
 
 	/* Search for (aligned) pointers. */
-	n = tal_len(p) / sizeof(void *);
+	n = tal_bytelen(p) / sizeof(void *);
 	for (i = 0; i < n; i++) {
 		void *ptr;