Don't need rustc_attr anymore

Author: nhamovitz

clippy_lints/src/lib.rs

@@ -21,7 +21,6 @@
 // (Currently there is no way to opt into sysroot crates without `extern crate`.)
 extern crate rustc_ast;
 extern crate rustc_ast_pretty;
-extern crate rustc_attr;
 extern crate rustc_data_structures;
 extern crate rustc_driver;
 extern crate rustc_errors;