BUILD: tools: remove obsolete and conflicting trace() from standard.c

Since commit 4c2ae48375 ("MINOR: trace: implement a very basic trace()
function") merged in 2.1, trace() is an inline function. It must not
appear in standard.c anymore and may break build depending on includes.

This can be backported to 2.1.

src/standard.c

@@ -4360,14 +4360,6 @@ int varint_bytes(uint64_t v)
 	return len;
 }
 
-/* do nothing, just a placeholder for debugging calls, the real one is in trace.c */
-#ifndef USE_OBSOLETE_LINKER
-__attribute__((weak,format(printf, 1, 2)))
-#endif
-void trace(char *msg, ...)
-{
-}
-
 /*
  * Local variables:
  *  c-indent-level: 8