memleak: add backtrace to allocations.

We use the tal notifiers to attach a `backtrace` object on every
allocation.

This also means moving backtrace_state from log.c into lightningd.c, so
we can hand it to memleak_init().

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

lightningd/log.h

@@ -95,7 +95,4 @@ const tal_t *ltmp;
 /* Before the crashlog is activated, just prints to stderr. */
 void NORETURN PRINTF_FMT(1,2) fatal(const char *fmt, ...);
 
-#if DEVELOPER
-extern bool dev_no_backtrace;
-#endif
 #endif /* LIGHTNING_LIGHTNINGD_LOG_H */