Remove definitions of deprecated Error::description() and Error::cause().

[briansmith]

No description provided.

[briansmith]

This seems like a SemVer breaking change so I'll defer to the next major version bump to do this.

[akhilles]

I don't think this is a breaking change at the API-level since Error::source() was introduced in Rust 1.30.0 (I'm assuming the MSRV of ring is > 1.30). Also, std::error::Error still provides default implementations for Error::description() and Error::cause():

fn description(&self) -> &str {
    "description() is deprecated; use Display"
}

fn cause(&self) -> Option<&dyn Error> {
    self.source()
}

The behavior of Error::cause() would be unaffected, but the description string would change from "ring::error::Unspecified" to "description() is deprecated; use Display". Would that be considered a breaking change?

[briansmith]

@akhilles Thanks for your help!