Remove `expire_access_token` from Docker configuration

[AaronDewes]

This value has been ignored since #5782, so there's no reason to keep it around in the docker homeserver.yaml.

Pull Request Checklist

• [x] Pull request is based on the develop branch
• [ ] Pull request includes a changelog file. The entry should:
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[CLAassistant]

All committers have signed the CLA.

[anoadragon453]

I've added a changelog so we can get this in.

Thanks again!