Update go to 1.18.9 and other misc cleanups

Update go and golangci-lint to more modern versions, and other changes related to that:

• Update go to version 1.18.9
• Update golangci-lint to 1.50.1
• Stop using ioutil package
• Remove deprecated linters
• Apply gofumpt to offending files
• Use go install instead of go get to install binaries.

Testing

As long at the pipeline continues to pass we're good.

Best reviewed commit-at-a-time