Also update golang.org/x/net and google.golang.org/grpc to fix vulnerabilities,
although cloudflared is using them in a way that is not exposed to those risks
This PR removes automatic assignees on github issues because it sends a
slightly wrong message about triaging. We will continue to triage issues
and find a more focussed method to nominate assignees.
This PR removes go-sumtype from cloudflared's build processes.
The value we see from analysing exhaustive match patterns in go is minimal (we can do this in code reviews) compared to using a tool that is unmaintained and (now broken) in Go 1.18.
We'd already been using the patched version here: https://github.com/sudarshan-reddy/go-sumtype because the original is broken for go tools > 1.16