Remove some unused features and `error-pattern`s

src/driver.rs

@@ -1,7 +1,4 @@
-// error-pattern:yummy
-#![feature(box_syntax)]
 #![feature(rustc_private)]
-#![allow(clippy::missing_docs_in_private_items)]
 
 // FIXME: switch to something more ergonomic here, once available.
 // (Currently there is no way to opt into sysroot crates without `extern crate`.)

src/lib.rs

@@ -1,7 +1,6 @@
 // error-pattern:cargo-clippy
 #![feature(plugin_registrar)]
 #![feature(rustc_private)]
-#![allow(clippy::missing_docs_in_private_items)]
 #![warn(rust_2018_idioms)]
 
 // FIXME: switch to something more ergonomic here, once available.

src/main.rs

@@ -1,8 +1,3 @@
-// error-pattern:yummy
-#![feature(box_syntax)]
-#![feature(rustc_private)]
-#![allow(clippy::missing_docs_in_private_items)]
-
 use rustc_tools_util::*;
 
 const CARGO_CLIPPY_HELP: &str = r#"Checks a package to catch common mistakes and improve your Rust code.