Remove unused `createCollection`

js/modules/migrations/migrations_0_database_with_attachment_data.js

@@ -1,6 +1,3 @@
-const isFunction = require('lodash/isFunction');
-const isObject = require('lodash/isObject');
-const isString = require('lodash/isString');
 const last = require('lodash/last');
 
 const { runMigrations } = require('./run_migrations');
@@ -153,24 +150,6 @@ const database = {
 exports.run = ({ Backbone } = {}) =>
   runMigrations({ Backbone, database });
 
-exports.createCollection = ({ Backbone, storeName }) => {
-  if (!isObject(Backbone) || !isObject(Backbone.Collection) ||
-      !isFunction(Backbone.Collection.extend)) {
-    throw new TypeError('"Backbone" is required');
-  }
-
-  if (!isString(storeName)) {
-    throw new TypeError('"database" is required');
-  }
-
-  const collection = new (Backbone.Collection.extend({
-    database,
-    storeName,
-  }))();
-
-  return collection;
-};
-
 exports.getDatabase = () => ({
   name: database.id,
   version: last(migrations).version,