RFC: Get rid of annotations

Annotations bring a complexity to the parser and the typechecker as well as unsatisfactory properties such as non-transitivity of type equality. They are useful when programming and debugging Michelson programs, but don't bring many strong guarantees, and aren't necessary once checked. Now that we have high-level languages targeting Michelson, annotations don't seem very useful to keep in the language.

Shall we just remove them?

If yes, we'll have to have discussions on:

• entrypoints
• migration & backward-compatibility