Move to-vfile defs to to-vfile repo

[phuctm97]

phuctm97.com/next-env.d.ts

Lines 9 to 17 in 2555d4e

	declare module "to-vfile" {
	import { VFile, VFileContents, VFileOptions } from "vfile";
	interface ToVFile {
	(input?: VFileContents | VFileOptions): VFile;
	readSync(path: string, encoding?: string): VFile;
	}
	const vfile: ToVFile;
	export default vfile;
	}

https://github.com/vfile/to-vfile