last-modified: remove double error message

When the user passes two revisions, they get the following output:

    $ git last-modified HEAD HEAD~
    error: last-modified can only operate on one revision at a time
    error: unable to setup last-modified

The error message about "unable to setup" is not very informative,
remove it.

Signed-off-by: Toon Claes <toon@iotcl.com>

Author: To1ne

builtin/last-modified.c

@@ -495,7 +495,7 @@ static int last_modified_init(struct last_modified *lm, struct repository *r,
 	lm->rev.bloom_filter_settings = get_bloom_filter_settings(lm->rev.repo);
 
 	if (populate_paths_from_revs(lm) < 0)
-		return error(_("unable to setup last-modified"));
+		return -1;
 
 	CALLOC_ARRAY(lm->all_paths, hashmap_get_size(&lm->paths));
 	lm->all_paths_nr = 0;