Remove CircleCI assets

[phani-srikar]

Description of changes

• Removes all the config files, scripts and metadata related to CircleCI setup.
• Removes the cb prefixes from the codebuild scripts.

Issue #, if available

Description of how you validated changes

The PR and E2E workflows are successful, see checks below.
Also tested the tag release flow with the changes.

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• Breaking changes to existing customers are released behind a feature flag or major version update
• Changes are tested using sample applications for all relevant platforms (iOS/android/flutter/Javascript) that use the feature added/modified

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.