subrepo: drop the default value of None for the archive matcher This was flagged by pytype after adding hints to `match.subdirmatcher` that it takes a non-optional matcher. That matcher argument is used without a guard in the subdirmatcher constructor, so that's the correct restriction. I don't think this fixes a bug in practice because the only way these are invoked is either by a parent `hgsubrepo.archive()`, `archival.archive()`, or the largefiles override of these. The `hgsubrepo.archive()` case (and the largefiles override) uses what the caller provided, so the caller will eventually be `archival.archive()` (or the largfiles override) up the call chain. The `archival.archive()` method also has None for its matcher's default arg. However, the three callers of that (`commands.archive()`, `webcommands.archive()`, and `extdiff.snapshot()`) all provide a matcher argument, so the None case can never occur unless a 3rd party extension swaps it for None. Sadly, we can't make the argument on the `archival.archive()` non-optional because there is a kwarg prior to it. Even though the largefiles override of `archival.archive()` is provided a valid matcher, we duplicate the internal creation of the matcher that the original `archival.archive()` does for consistency. By eliminating an impossible to hit case, we can simplify some of the subrepo code too, by dropping unreachable code.