std: remove unused linker attribute

Author: joboet

Diff for: library/std/src/sys/unix/thread_parker/darwin.rs

@@ -24,7 +24,7 @@ type dispatch_time_t = u64;
 const DISPATCH_TIME_NOW: dispatch_time_t = 0;
 const DISPATCH_TIME_FOREVER: dispatch_time_t = !0;
 
-#[link(name = "System", kind = "dylib")]
+// Contained in libSystem.dylib, which is linked by default.
 extern "C" {
     fn dispatch_time(when: dispatch_time_t, delta: i64) -> dispatch_time_t;
     fn dispatch_semaphore_create(val: isize) -> dispatch_semaphore_t;