Do not export methods

[ehmicky]

I think methods should remain an internal representation of the OpenAPI specification. Exporting it makes it harder to change that internal representation without introducing breaking changes.

Users that need to know which methods we expose should either:

• use Object.keys(NetlifyAPI.prototype)
• require @netlify/open-api

There are currently no public repositories that use that exported variable on GitHub, except our own repositories. So we would need to modify it in our repositories, then make a major release.