Update build tools including Go 1.16.2

[bboreham]

• Stop creating a NodeJS build image, just use node:10.19 directly.
• Update to Go 1.16.2.
• Remove some unused tools.
• Fix some build issues on MacOS.
• Add 'osusergo' tag to remove some link-time warnings.
• Remove 'demo.json' file, not used in Scope.
• Miscelaneous other build improvements.

[dholbach]

Great work - this looks much cleaner now! Some cursory local testing went well as well!