reftable: ignore unused argc/argv in test functions

reftable: ignore unused argc/argv in test functions

There are several reftable test "main" functions that don't look at
their argc/argv. They don't technically need to take these parameters,
as they are called individually by cmd__reftable(). But it probably
makes sense to keep them all consistent for now. In the long run these
will probably all get converted to the unit-test framework anyway.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>