remove docker action

[sbfnk]

Description

This PR closes #864 by removing the action altogether.

Presumably we can also remove the .devcontainer directory?

Initial submission checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have tested my changes locally (using devtools::test() and devtools::check()).
• I have added or updated unit tests where necessary.
• I have updated the documentation if required and rebuilt docs if yes (using devtools::document()).
• I have followed the established coding standards (and checked using lintr::lint_package()).
• I have added a news item linked to this PR.

After the initial Pull Request

• I have reviewed Checks for this PR and addressed any issues as far as I am able.

[jamesmbaazam]

Presumably we can also remove the .devcontainer directory?

Yes.

[seabbs]

We should also remove the out of date built images so people don't accidently use them. @jamesmbaazam I tagged you to review as the unfortunate first responder - happy to do it if you are rushed