Clean up workaround that required too many parentheses

The issue has been fixed in the compiler and these extra call site parentheses
are no longer required.

test_suite/no_std/src/main.rs

@@ -9,10 +9,6 @@
 #![feature(lang_items, start, compiler_builtins_lib)]
 #![no_std]
 
-// https://github.com/rust-lang/rust/issues/47311
-#![allow(unused_parens)]
-#![cfg_attr(feature = "cargo-clippy", allow(double_parens))]
-
 extern crate libc;
 extern crate compiler_builtins;