Remove the "linked_from" feature.

src/test/compile-fail/feature-gate-linked-from.rs

@@ -1,16 +0,0 @@
-// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-#[linked_from = "foo"] //~ ERROR experimental feature
-extern {
-    fn foo();
-}
-
-fn main() {}

src/test/run-make/issue-15460/foo.rs

@@ -8,11 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(linked_from)]
 #![crate_type = "dylib"]
 
 #[link(name = "foo", kind = "static")]
-#[linked_from = "foo"]
 extern {
     pub fn foo();
 }

src/test/run-pass/auxiliary/issue-25185-1.rs

@@ -10,12 +10,9 @@
 
 // no-prefer-dynamic
 
-#![feature(linked_from)]
-
 #![crate_type = "rlib"]
 
 #[link(name = "rust_test_helpers", kind = "static")]
-#[linked_from = "rust_test_helpers"]
 extern {
     pub fn rust_dbg_extern_identity_u32(u: u32) -> u32;
 }