Remove bootstrap step from this command so it's easier to run on Heroku (#3676)

Heroku has a 60 second limit on app startup time, so this command
shouldn't attempt to do any bootstrapping.

Author: m-allanson

packages/gatsby/src/commands/data-explorer.js

@@ -3,15 +3,12 @@
 const express = require(`express`)
 const graphqlHTTP = require(`express-graphql`)
 const { store } = require(`../redux`)
-const bootstrap = require(`../bootstrap`)
 
+// Note: the store must exist already. Create it with `gatsby build`.
 module.exports = async (program: any) => {
   let { port, host } = program
   port = typeof port === `string` ? parseInt(port, 10) : port
 
-  // bootstrap to ensure schema is in the store
-  await bootstrap(program)
-
   const app = express()
   app.use(
     `/`,