Undefine module support

Duktape has some shims for CJS style modules. However, its pretty useless in the context of this extension since you still need to write some c code to tell the module loader how to read files from disk. That leaves a broken `require` as global function. Its typical for JS libraries to test for `require` and `module` and change behavior in a CJS environment.

It might be interesting to implement the module loader stuff someday, but for now I think we should just remove them and normalize the default context.