Revert "[Refactor] deprecated lib/core.js now uses data from is-core-module also"

This reverts commit 122bb64.

Fixes #297.

Author: ljharb

lib/core.js

@@ -1,9 +1,7 @@
 'use strict';
 
 var isCoreModule = require('is-core-module');
-var path = require('path');
-var fs = require('fs');
-var data = JSON.parse(String(fs.readFileSync(path.join(path.dirname(require.resolve('is-core-module/package.json')), 'core.json'))));
+var data = require('./core.json');
 
 var core = {};
 for (var mod in data) { // eslint-disable-line no-restricted-syntax