Behind names for types make no sense

[dahlia]

Unlike fields, tags, methods, and method parameters, type names don't play any role in transportation. Types have names, and "_type" hint field in serialization format, but they're only for human programmers. These "_type" hints are ignored when a program interprets a serialized value.

So the parser should disallow to add a behind name to type declarations.

Currently it even raises an error if two types have the same behind name (but two different facial names) for no reason:

record foo/dup (text x);
record bar/dup (text y);

examples/type-behind-name.nrm:4:1:
the behind type name `dup` is duplicated


^

[dahlia]

It might be better to remove "_type" field too?