Remove cargo-audit ignores

The advisories have been withdrawn since they don't seem to be security
critical and the problem goes all the way down to the POSIX API.

See rustsec/advisory-db#1190

.github/workflows/ci.yml

@@ -35,4 +35,4 @@ jobs:
  steps:
  - uses: actions/checkout@v2
  - run: pacman --noconfirm -Sy cargo-audit
- - run: cargo audit --ignore RUSTSEC-2020-0071 --ignore RUSTSEC-2020-0159
+ - run: cargo audit