[#18] Update cross references checker in CI

Problem: crossref-verifier that we are using has been updated and it brings several improvements we can use:

1. Now it has releases with static binaries that we can download and use on CI without building anything.
2. It no longer requires a config, now it has a default one that suits our needs.
3. Encoding issues have been fixed.

Solution: update CI config to download xrefcheck-0.1.1 and run it. Remove crossref-verifier.yaml as it's no longer necessary.

Fixes #18 (closed).