remove docker image specification

[ceschae]

Description

CI for this repo is broken, following recommended remediation:

Job was rejected because this version of Docker is not supported on this resource class. Try removing the version of Docker in your .circleci/config.yml and re-running

TODOs

Please ensure all of these TODOs are completed before asking for a review.

• Ensure the branch is named correctly with the issue number. e.g: feature/new-vpc-endpoints-955 or bug/missing-count-param-434.
• Update the docs.
• Keep the changes backward compatible where possible.
• Run the pre-commit checks successfully.
• Run the relevant tests successfully.
• Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.