Fixes nightly compilation problems where the "hash_drain_filter" feature got renamed to "hash_extract_if".

See rust-lang/rust#104455 for more info.

…igning

certificates.

Currently, the `Vec::extract_if` iterator is never consumed, which results in
no operation being performed and breaks hyperpom. Since we don't
actually use the handles that are removed, a simple solution is
to use `Vec::retain` instead (which should have been the original
solution to the problem anyway).

…ion to make sure we don't run into rust-lang/rust#113152

Simpler build system and replacing `Vec::extract_if` with `Vec::retain`