No longer parse it.
Remove AutoTrait variant from AST and HIR.
Remove backwards compatibility lint.
Remove coherence checks, they make no sense for the new syntax.
Remove from rustdoc.
Trait's implementations with private type parameters were displayed in
the implementing struct's documentation until now.
With this change any trait implementation that uses a private type
parameter is now hidden in the docs.
DefaultImpl is a highly confusing name for what we now call auto impls,
as in `impl Send for ..`. The name auto impl is not formally decided
but for sanity anything is better than `DefaultImpl` which refers
neither to `default impl` nor to `impl Default`.
This attribute has two effects:
1. Items with this attribute and their children will have the "This is
supported on **** only" message attached in the documentation.
2. The items' doc tests will be skipped if the configuration does not
match.
* Make sure private consts are stripped.
* Don't show a code block for the value if there is none.
* Make sure default values are shown in impls.
* Make sure docs from the trait are used if the impl has no docs.
