Accept interpolated patterns in trait method parameters
Permit this, basically
```rust
macro_rules! m {
($pat: pat) => {
trait Tr {
fn f($pat: u8) {}
}
}
}
```
it previously caused a parsing error during expansion because trait methods accept only very restricted set of patterns during parsing due to ambiguities caused by [anonymous parameters](https://github.com/rust-lang/rust/issues/41686), and this set didn't include interpolated patterns.
Some outdated messages from "no patterns allowed" errors are also removed.
Addresses https://github.com/rust-lang/rust/issues/35203#issuecomment-341937159
b22679366a