Revert hacks to get the specialisation preview release to build

[epost]

• Stop overriding the typedefs npm package by an included bundle file: https://github.com/typedefs/try-typedefs/pull/23/files#diff-a89910110c5c8700a71e3c918d7ef28cR3
• simplify the build? it's a bit of a legacy mess of files atm.

/cc @andrevidela