Fix Flow.

Removed `@flow` annotation from files that don't actually pass Flow check at the moment. These will be added back file by file once the files are properly converted to use Flow.

Closes #3064

src/parser/statement.js

@@ -1,5 +1,3 @@
-/* @flow */
-
 import { types as tt } from "../tokenizer/types";
 import Parser from "./index";
 import { lineBreak } from "../util/whitespace";