Removes ignore_column for file_checksum

What does this MR do and why?

Relates to #500465 (closed).

This MR is the final step of the multi-release approach, which cleans up and removes the ignore rule for file_checksum in the xray_report model.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

ee/app/models/projects/xray_report.rb

@@ -3,9 +3,6 @@
 module Projects
   class XrayReport < ApplicationRecord
     include Gitlab::Utils::StrongMemoize
-    include IgnorableColumns
-
-    ignore_column :file_checksum, remove_with: '17.8', remove_after: '2024-12-22'
 
     belongs_to :project