lib: remove useless statement

There's no need to set 'false' to 'isAsync' because we've declared it
before.

PR-URL: #39983
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>

lib/internal/streams/from.js

@@ -25,7 +25,7 @@ function from(Readable, iterable, opts) {
     });
   }
 
-  let isAsync = false;
+  let isAsync;
   if (iterable && iterable[SymbolAsyncIterator]) {
     isAsync = true;
     iterator = iterable[SymbolAsyncIterator]();