metamask-extension/app/scripts/migrations/035.js

// next version number
/*

Removes the deprecated 'seedWords' state

*/

import { cloneDeep } from 'lodash'

const version = 35

export default {
  version,

  async migrate(originalVersionedData) {
    const versionedData = cloneDeep(originalVersionedData)
    versionedData.meta.version = version
    versionedData.data = transformState(versionedData.data)
    return versionedData
  },
}

function transformState(state) {
  if (
    state.PreferencesController &&
    state.PreferencesController.seedWords !== undefined
  ) {
    delete state.PreferencesController.seedWords
  }
  return state
}