This will utilize the superstate's error object in place of nested errors,
which was the result of the previous composition-based delegation.
As you can see, all we had to do was remove the special handling of these
errors; the existing delegation setup continues to handle the types properly
with no change. The composition continues to work for `*Attr_`.
The alternative was to box inner errors, since they're far from the hot code
path, but that's clearly unnecessary.
To be clear: this is necessary to allow for recursive grammars in
`ele_parse` without creating recursive data structures in Rust.
DEV-7145
Mike Gerwitz
4aaf91a9e7