Backport 2.28: Set psk to NULL in ssl_psk_remove

[lhuang04]

Summary: Back port PR 9241 to 2.28 branch

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:

Description

Please write a few sentences describing the overall goals of the pull request's commits.

PR checklist

Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")

• [ ] changelog provided, or not required
• [ ] 3.6 backport done, or not required
• [x] 2.28 backport done, or not required
• [ ] tests provided, or not required

Notes for the submitter

Please refer to the contributing guidelines, especially the checklist for PR contributors.

Help make review efficient:

• Multiple simple commits
  • please structure your PR into a series of small commits, each of which does one thing
• Avoid force-push
  • please do not force-push to update your PR - just add new commit(s)
• See our Guidelines for Contributors for more details about the review process.