Update EOL message about builder image updates (#93)

Updates the EOL message to reflect that we're now stopping
updating these images. I've also removed the explicit builder
image name example from the message, since it will get out of
date once future builders are released.

This is the cnb-shim equivalent of:
heroku/cnb-builder-images#513

Towards:
heroku/cnb-builder-images#512.

bin/build

@@ -54,10 +54,9 @@ if [[ "${STACK}" == "heroku-"* ]]; then
 
 		In addition, the legacy builder images that use shimmed buildpacks
 		(such as 'heroku/buildpacks:20' or 'heroku/builder-classic:22') are
-		no longer supported and will soon stop receiving security updates.
+		no longer supported and do not receive any security updates or fixes.
 
-		Please switch to one of our newer 'heroku/builder:*' builder images,
-		such as 'heroku/builder:22':
+		Please switch to one of our newer 'heroku/builder:*' builder images:
 		https://github.com/heroku/cnb-builder-images#available-images
 
 		If you are using the Pack CLI, you will need to adjust your '--builder'