chore(gatsby): Get rid of "DeprecationWarning: asynchronous function …

…without callback" (gatsbyjs#13209)

* Get rid of DeprecationWarning: Calling an asynchronous function without callback is deprecated

* Move to fs-extra remove for simplicity

packages/gatsby/src/commands/build-html.js

@@ -1,6 +1,6 @@
 /* @flow */
 const webpack = require(`webpack`)
-const fs = require(`fs`)
+const fs = require(`fs-extra`)
 
 const webpackConfig = require(`../utils/webpack.config`)
 const { createErrorFromString } = require(`gatsby-cli/lib/reporter/errors`)
@@ -44,8 +44,8 @@ const buildRenderer = async (program, stage) => {
 
 const deleteRenderer = async rendererPath => {
   try {
-    await fs.unlink(rendererPath)
-    await fs.unlink(`${rendererPath}.map`)
+    await fs.remove(rendererPath)
+    await fs.remove(`${rendererPath}.map`)
   } catch (e) {
     // This function will fail on Windows with no further consequences.
   }