remove some unnecessary feature flags

Author: RalfJung

tests/compile-fail/check_arg_count_too_few_args.rs

@@ -1,5 +1,4 @@
 #![feature(core_intrinsics)]
-#![feature(rustc_private)]
 
 fn main() {
     extern "C" {

tests/compile-fail/check_arg_count_too_many_args.rs

@@ -1,5 +1,4 @@
 #![feature(core_intrinsics)]
-#![feature(rustc_private)]
 
 fn main() {
     extern "C" {

tests/compile-fail/shim_arg_size.rs

@@ -1,5 +1,3 @@
-#![feature(rustc_private)]
-
 fn main() {
     extern "C" {
         // Use the wrong type(ie. not the pointer width) for the `size`

tests/run-pass/calloc.rs

@@ -2,10 +2,10 @@
 
 #![feature(rustc_private)]
 
-use core::slice;
-
 extern crate libc;
 
+use core::slice;
+
 fn main() {
     unsafe {
         let p1 = libc::calloc(0, 0);

tests/run-pass/fs.rs

@@ -3,15 +3,15 @@
 
 #![feature(rustc_private)]
 
+extern crate libc;
+
 use std::fs::{
     File, create_dir, OpenOptions, read_dir, remove_dir, remove_dir_all, remove_file, rename,
 };
 use std::ffi::CString;
 use std::io::{Read, Write, Error, ErrorKind, Result, Seek, SeekFrom};
 use std::path::{PathBuf, Path};
 
-extern crate libc;
-
 
 fn main() {
     test_file();

tests/run-pass/malloc.rs

@@ -2,10 +2,10 @@
 
 #![feature(rustc_private)]
 
-use core::{slice, ptr};
-
 extern crate libc;
 
+use core::{slice, ptr};
+
 fn main() {
     // Test that small allocations sometimes *are* not very aligned.
     let saw_unaligned = (0..64).any(|_| unsafe {

tests/run-pass/regions-mock-trans.rs

@@ -3,6 +3,7 @@
 #![feature(rustc_private)]
 
 extern crate libc;
+
 use std::mem;
 
 struct Arena(());