bin: remove version check that does not work

bin/check-npm-version.js

@@ -1,19 +0,0 @@
-#!/usr/bin/env node
-
-'use strict'
-
-const userAgent = process.env.npm_config_user_agent
-if (!userAgent) {
-  // not much we can do
-  process.exit()
-}
-
-if (/^npm\/7/.test(userAgent)) {
-  console.error('Please use npm 6 to work in the Uppy monorepo.')
-  console.error('You can execute individual commands with npm 6 like below:')
-  console.error()
-  console.error('  $ npx npm@6 install')
-  console.error()
-  console.error('This way you can still use npm 7 in your other projects.')
-  process.exit(1)
-}

package.json

@@ -234,7 +234,6 @@
     "lint:markdown": "remark -f -q . -i .gitignore",
     "lint:staged": "lint-staged",
     "lint": "eslint . --cache",
-    "preinstall": "node ./bin/check-npm-version.js",
     "release": "bash ./bin/release",
     "size": "echo 'JS Bundle mingz:' && cat ./packages/uppy/dist/uppy.min.js | gzip | wc -c && echo 'CSS Bundle mingz:' && cat ./packages/uppy/dist/uppy.min.css | gzip | wc -c",
     "start:companion": "bash ./bin/companion",