Remove some of the older obsolete syntax things

[nrc]

They clutter up the parser and are confusing for new users. We should remove obsolete syntax once it is no longer useful. We should audit these during the beta period.

[sfackler]

We might just want to remove all obsolete syntax for 1.0.

[nrc]

I would not be opposed to that

[aochagavia]

Would it be possible to make a list of things that need to be removed (e.g. enum variants, functions, etc)? That way it would be easier for others (like me) to help.

[nrc]

I'm talking in particular about the things in https://github.com/rust-lang/rust/blob/master/src/libsyntax/parse/obsolete.rs I.e., syntax which has been removed, but still gives specific obsolete errors, rather than generic syntax errors.