Remove Packages::Composer::CacheFile and related code

Context

In Remove composer cache files related code (!159861 - merged) we removed the composer cache file related code but left the ActiveRecord model Packages::Composer::CacheFile, the uploader Packages::Composer::CacheUploader and added the background migration to remove the entries from the packages_composer_cache_files table.

In Finalize DeletePackagesComposerCacheFileRecords... (!162995 - merged) the background migration was finalized.

Now, when the database table is empty, we could go ahead and delete the application code.

What does this MR do and why?

This MR removes Packages::Composer::CacheFile model and related code:

• Remove Packages::Composer::CacheUploader uploader.
• Remove the batched background migration.
• Turn the database migrations into no operations.

The next MR will remove the database table Remove database table packages_composer_cache_f... (!159904 - merged)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

No.

How to set up and validate locally

Nothing really to test apart from validating that some classes don't present anymore: Packages::Composer::CacheFile and Packages::Composer::CacheUploader.

Related to #461786 (closed)