remove unnecessary lib

app/scripts/controllers/transactions/tx-state-manager.js

@@ -2,7 +2,6 @@ const extend = require('xtend')
 const EventEmitter = require('events')
 const ObservableStore = require('obs-store')
 const ethUtil = require('ethereumjs-util')
-const log = require('loglevel')
 const txStateHistoryHelper = require('./lib/tx-state-history-helper')
 const createId = require('../../lib/random-id')
 const { getFinalStates } = require('./lib/util')