match: remove doc about undefined behavior of visitdir()...
match: remove doc about undefined behavior of visitdir()
This was added by 8545bd381504, but core matchers support visitdir() of
arbitrary locations since 2773540c3650, and verifier._verifymanifest()
doesn't seem to strictly obey the restriction.
I have no idea how important this API contract is for third-party extensions.
That's why this patch is RFC.
