fix Flow failure breaking yarn run build

Summary:
`flow-api-translator` can't handle `module.exports`. Simplest fix is to not identify
the bridging file (that we use to register with babel to transpile when run directly)
as a flow file.

Changelog: [Internal] - Fixing an internal build script broken by D56243647

Differential Revision: D56638506

packages/core-cli-utils/src/index.js

@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
  * @format
  * @oncall react_native
  */