change go_json to not escape <, &, >

...and ditch json.MarshalNoEscape().
This because we don't really want escaped HTML related characters anyway.
This will probably buy us a few clock cycles and also make go_json simpler.
As part of this effort, we need to fix all the go_json tests, which currently expect escaped <, &, > and will have to be switched to the literal characters.

Filed under query because we don't have a go_json component.