Don't perform extra go env calls in go/packages.
Load only needed go env vars in golangci-lint.
Stay in sync by enabled analyzers in go vet: remove nilness and
atomicalign analyzers, add errorsas analyzer.
Don't build SSA for govet.
Standalone govet runs 25% faster than before. All runs can be 5-10% faster
than before.
Relates: #208