Move the iD.data export from data/index.js to coreData

coreData now owns all the data, and data/index.js should eventually go away
(re: #4994)

data/index.js

@@ -1,4 +1,2 @@
 export { dataLocales } from './locales.json';
 export { en as dataEn } from '../dist/locales/en.json';
-
-export let data = {};

modules/core/data.js

@@ -1,6 +1,7 @@
 import { json as d3_json } from 'd3-fetch';
-import { data as _data } from '../../data';  // prebundled data
 
+let _data = {};
+export { _data as data };
 
 //
 // The coreData module fetches data from JSON files

modules/core/index.js

@@ -1,5 +1,5 @@
 export { coreContext } from './context';
-export { coreData } from './data';
+export { data, coreData } from './data';
 export { coreDifference } from './difference';
 export { coreGraph } from './graph';
 export { coreHistory } from './history';