PR Opened: Remove Label after Has PR is added

[hzoo]

Add Has PR label to issues that have been referenced in a PR

After

babel-bot/src/handlers/pull_request/opened.js

Line 46 in 635399d

const requests = issues.map(id => github.addLabels(

Remove help wanted label

---

Same if someone claims an issue?

help-wanted -> claimed -> Has PR?