Revert "Ensure that passwords are never long enough for a DoS."

This reverts commit aae5a96d5754ad34e48b7f673ef2411a3bbc1015.

This fix is no longer necessary, our pbkdf2 (see next commit) implementation
no longer rehashes the password every iteration.
Fixed #21138 -- Increased the performance of our PBKDF2 implementation.

Thanks go to Michael Gebetsroither for pointing out this issue and help on
the patch.