doc: unify ERR_FALSY_VALUE_REJECTION description

PR-URL: #13869
Refs: #13604
Refs: #13627
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/errors.md

@@ -577,8 +577,8 @@ Used when `Console` is instantiated without `stdout` stream or when `stdout` or
 <a id="ERR_FALSY_VALUE_REJECTION"></a>
 ### ERR_FALSY_VALUE_REJECTION
 
-The `ERR_FALSY_VALUE_REJECTION` error code is used by the `util.callbackify()`
-API when a callbackified `Promise` is rejected with a falsy value (e.g. `null`).
+Used by the `util.callbackify()` API when a callbackified `Promise` is rejected
+with a falsy value (e.g. `null`).
 
 <a id="ERR_INDEX_OUT_OF_RANGE"></a>
 ### ERR_INDEX_OUT_OF_RANGE