Revert "Update ImageBuilder to track layers in VersionInfo (#2524)" (#2525)

This reverts commit 5aca28d.

Author: MichaelSimons

eng/common/templates/variables/docker-images.yml

@@ -1,5 +1,5 @@
 variables:
-  imageNames.imageBuilder: mcr.microsoft.com/dotnet-buildtools/image-builder:957042
+  imageNames.imageBuilder: mcr.microsoft.com/dotnet-buildtools/image-builder:939194
   imageNames.imageBuilder.withrepo: imagebuilder-withrepo:$(Build.BuildId)-$(System.JobId)
   imageNames.testRunner: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-stretch-slim-docker-testrunner-690072
   imageNames.testRunner.withrepo: testrunner-withrepo:$(Build.BuildId)-$(System.JobId)