Fix stable_features warning

``` error: the feature `cfg_target_has_atomic` has been stable since 1.60.0 and no longer requires an attribute to enable --> futures/tests/no-std/src/lib.rs:3:12 | 3 | #![feature(cfg_target_has_atomic)] | ^^^^^^^^^^^^^^^^^^^^^ ```
rust-lang · Feb 16, 2022 · a174117 · a174117
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commit a174117
Showing 1 changed file with 0 additions and 1 deletion.
diff --git a/futures/tests/no-std/src/lib.rs b/futures/tests/no-std/src/lib.rs
@@ -1,6 +1,5 @@
 #![cfg(nightly)]
 #![no_std]
-#![feature(cfg_target_has_atomic)]
 
 #[cfg(feature = "futures-core-alloc")]
 #[cfg(target_has_atomic = "ptr")]