chore: Improve two integration tests

[jbelkins]

Description of changes

• The MediaConvert service no longer requires endpoint discovery; the regional endpoint accepts requests directly. Code to request a MediaConvert endpoint is removed.
• The time delay while waiting for a CloudFront KVS to provision is reduced from 20 to 2.5 seconds, to avoid unneeded wait during test runs.

New/existing dependencies impact assessment, if applicable

No new dependencies were added to this change.

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