merge-recursive: do not report the resulting tree object name

It is not available in the outermost merge, and it is only
useful for debugging merge-recursive in the inner merges.

Sergey Vlasov noticed that the old code accesses an
uninitialized location.

Signed-off-by: Junio C Hamano <junkio@cox.net>

merge-recursive.c

@@ -1066,13 +1066,10 @@ static int merge_trees(struct tree *head,
 		path_list_clear(re_head, 0);
 		path_list_clear(entries, 1);
 
-	} else {
-		clean = 1;
-		printf("merging of trees %s and %s resulted in %s\n",
-		       sha1_to_hex(head->object.sha1),
-		       sha1_to_hex(merge->object.sha1),
-		       sha1_to_hex((*result)->object.sha1));
 	}
+	else
+		clean = 1;
+
 	if (index_only)
 		*result = git_write_tree();