NEWS.md: remove nonsense caveat

3.0 will be released in a few days (hopefully), so remove a caution: "it
may be reverted until 3.0 release."

NEWS.md

@@ -476,9 +476,6 @@ Excluding feature bug fixes.
     * Now `{ a: 1 }.each(&->(k, v) { })` raises an ArgumentError
       due to lambda's arity check.
 
-    * This is experimental; if it brings a big incompatibility issue,
-      it may be reverted until 3.0 release.
-
 * When writing to STDOUT redirected to a closed pipe, no broken pipe
   error message will be shown now.  [[Feature #14413]]