cfn2ts: stop generating attribute types altogether

[eladb]

We got rid of most attribute types as we introduced token stringification (#24). We still have some attribute types generated for non strings, but those are fringy, and I believe we can just leave them as Token | Primitive types.

One reason to get rid of those is because they can are currently generated outside the cloudformation namespace and effectively cause cycle reference between the L2 code (which depends on "cloudformation.Xxx") and the code under the "cloudformation" namespace (which depends on those generated attributes). In TypeScript that's not an issue, but it appears this causing problems for Python for example (and in general a bad practice).

Copy @dstufft

[eladb]

Implemented in #1493