Drop image compress step when building 16.0

What does this MR do and why?

Drops the image compression script when building the 16.0 branch.

This script appears to be causing pipeline failures on the 16.0 branch, even after refactoring the script to not error (!4928 (merged)), and also dropping the flag that could throw an "exit code 98" (!4929 (merged)).

This is not ideal, but the 16.0 site will still be functional without compressed images, and we need to get a fix backported, so let's try dropping the compress images step.

• Dropping it from single.Dockerfile will make it no longer run on the docker image test jobs (which are the actual failures)
• Dropping it from 16.0.Dockerfile will make it no longer run when building 16.0's archive images. In theory if it's failing on the test it'd eventually fail here as well.

How to set up and validate locally

n/a

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.