read-tree: "read-tree -m --empty" does not make sense

fb1bb96 ("read-tree: deprecate syntax without tree-ish args",
2010-09-10) wanted to deprecate "git read-tree" without any tree,
which used to be the way to empty the index, and encourage use of
"git read-tree --empty" instead.

However, when used with "-m", "--empty" does not make any sense,
either, simply because merging 0 trees will result in a different
error anyway.

Omit the deprecation warning and let the code to emit real error
message diagnose the error.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

builtin/read-tree.c

@@ -181,7 +181,7 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 			die("failed to unpack tree object %s", arg);
 		stage++;
 	}
-	if (nr_trees == 0 && !read_empty)
+	if (!nr_trees && !read_empty && !opts.merge)
 		warning("read-tree: emptying the index with no arguments is deprecated; use --empty");
 	else if (nr_trees > 0 && read_empty)
 		die("passing trees as arguments contradicts --empty");