Remove task_unsupervise from rt builtin functions

This was an exact duplicate of the unsupervise function

src/lib/task.rs

@@ -2,7 +2,7 @@ native "rust" mod rustrt {
     fn task_sleep(uint time_in_us);
     fn task_yield();
     fn task_join(task t) -> int;
-    fn task_unsupervise();
+    fn unsupervise();
     fn pin_task();
     fn unpin_task();
 }
@@ -33,7 +33,7 @@ fn join(task t) -> task_result {
 }
 
 fn unsupervise() {
-    ret rustrt::task_unsupervise();
+    ret rustrt::unsupervise();
 }
 
 fn pin() {

src/rt/rust_builtin.cpp

@@ -430,11 +430,6 @@ task_join(rust_task *task, rust_task *join_task) {
     }
 }
 
-extern "C" CDECL void
-task_unsupervise(rust_task *task) {
-    task->unsupervise();
-}
-
 /* Debug builtins for std.dbg. */
 
 static void

src/rt/rustrt.def.in

@@ -50,7 +50,6 @@ str_vec
 task_sleep
 task_yield
 task_join
-task_unsupervise
 unsafe_vec_to_mut
 unsupervise
 upcall_clone_chan