Remove test of static Context

Context is no longer Sync so this doesn't work.

    error[E0277]: `*mut ()` cannot be shared between threads safely
      --> library/core/tests/task.rs:24:21
       |
    24 |     static CONTEXT: Context<'static> = Context::from_waker(&WAKER);
       |                     ^^^^^^^^^^^^^^^^ `*mut ()` cannot be shared between threads safely
       |
       = help: within `Context<'static>`, the trait `Sync` is not implemented for `*mut ()`
       = note: required because it appears within the type `PhantomData<*mut ()>`
       = note: required because it appears within the type `Context<'static>`
       = note: shared static variables must have a type that implements `Sync`

library/core/tests/task.rs

@@ -1,4 +1,4 @@
-use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
+use core::task::{Poll, RawWaker, RawWakerVTable, Waker};
 
 #[test]
 fn poll_const() {
@@ -21,9 +21,5 @@ fn waker_const() {
 
     static WAKER: Waker = unsafe { Waker::from_raw(VOID_WAKER) };
 
-    static CONTEXT: Context<'static> = Context::from_waker(&WAKER);
-
-    static WAKER_REF: &'static Waker = CONTEXT.waker();
-
-    WAKER_REF.wake_by_ref();
+    WAKER.wake_by_ref();
 }