Use a new flag `--npm-publish` in conjunction with `publish` action,
so that the default will always be to `npm pack` if the new flag is not
specified. This flag is also guarded in the actual npm publish code to
ensure that it can only run in the appropriate CI alpha/beta/stable
environment, and not in local or test.
This then also removes the separate `pack` action.
Also removes legacy boilerplate from a number of build scripts.