Stabilize #[repr(transparent)]

Tracking issue FCP: https://github.com/rust-lang/rust/issues/43036#issuecomment-394094318
Reference PR: https://github.com/rust-lang-nursery/reference/pull/353

src/test/codegen/repr-transparent-aggregates-1.rs

@@ -18,7 +18,6 @@
 // See repr-transparent.rs
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 
 #[repr(C)]

src/test/codegen/repr-transparent-aggregates-2.rs

@@ -22,7 +22,6 @@
 // See repr-transparent.rs
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 
 #[repr(C)]

src/test/codegen/repr-transparent-aggregates-3.rs

@@ -14,7 +14,6 @@
 // See repr-transparent.rs
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 
 #[repr(C)]

src/test/codegen/repr-transparent-sysv64.rs

@@ -13,7 +13,6 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type="lib"]
-#![feature(repr_transparent)]
 
 #[repr(C)]
 pub struct Rgb8 { r: u8, g: u8, b: u8 }

src/test/codegen/repr-transparent.rs

@@ -11,7 +11,7 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type="lib"]
-#![feature(repr_transparent, repr_simd)]
+#![feature(repr_simd)]
 
 use std::marker::PhantomData;