Ubuntu helix images are way too big

```
mcr.microsoft.com/dotnet-buildtools/prereqs azurelinux-3.0-helix-amd64 3adf959b24f4 12 days ago 590MB
mcr.microsoft.com/dotnet-buildtools/prereqs ubuntu-24.04-helix-amd64 9a5876c412a2 13 days ago 1.97GB
```

while providing same functionally the Ubuntu seems disproportionally bigger. It takes 1-2 minutes on Job run to pull and instantiate container and based on my testing the AZL is 1/3 of the time e.g. proportional to the size. We are creating unnecessary network and I/O load.

The problem does not exist if same container runs again but the VM instances are created ad-hoc by VMMS scaler and there is also aggressive cleanup to prevent disk exhaustion. Trimming the image may be quite simple and can save lot of resources.

Also, other Helix images may have similar problem.

No file or test is named. Start by locating the Dockerfile or build context for ubuntu-24.04-helix-amd64, compare it with azurelinux-3.0-helix-amd64, and measure the resulting image size; done means reducing unnecessary image content without losing the same functionality, while checking whether other Helix images have the same issue.

Written by the indexing model from the issue text.