tree-walk: lose base_offset that is never used in tree_entry_interesting

The tree_entry_interesting() function takes base_offset, allowing
its callers to potentially pass a non-zero number to skip the early
part of the path string.

The feature is never exercised and we do not even know what bugs are
lurking there, as all callers pass 0 to the parameter.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

tree-diff.c

@@ -316,7 +316,7 @@ static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
 
 	while (t->size) {
 		match = tree_entry_interesting(opt->repo->index, &t->entry,
-					       base, 0, &opt->pathspec);
+					       base, &opt->pathspec);
 		if (match) {
 			if (match == all_entries_not_interesting)
 				t->size = 0;