metamask-extension/app/scripts/migrations/040.js

import { cloneDeep } from 'lodash';

const version = 40;

/**
 * Site connections are now managed by the PermissionsController, and the
 * ProviderApprovalController is removed. This migration deletes all
 * ProviderApprovalController state.
 */
export default {
  version,
  async migrate(originalVersionedData) {
    const versionedData = cloneDeep(originalVersionedData);
    versionedData.meta.version = version;
    const state = versionedData.data;
    versionedData.data = transformState(state);
    return versionedData;
  },
};

function transformState(state) {
  delete state.ProviderApprovalController;
  return state;
}