Avoid the explicit Equatable conformance if already conforming to Hashable

[czechboy0]

Avoid the explicit Equatable conformance if already conforming to Hashable.

Both in our codebase and in the generated code - any type that conforms to Hashable doesn't need the extra explicit conformance to Equatable.

[czechboy0]

Let's keep it open until the runtime library changes land too: #214 (comment)