Remove FK dast_site_profiles_builds.ci_build_id as we have LFK

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/77908 we
already added a ["loose foreign key"](
https://docs.gitlab.com/ee/development/database/loose_foreign_keys.html)
to replace this foreign key. Now that this has been running fine in
production we should be OK to remove the foreign key altogether.

This was added in a post-deployment migration as we want to ensure that
they have the correct code running with the loose foreign key in place
before we remove the foreign key to ensure that there isn't any lost
deletes.

Changelog: other

db/post_migrate/20220110233155_remove_dast_site_profiles_builds_ci_build_id_fk.rb

+# frozen_string_literal: true
+
+class RemoveDastSiteProfilesBuildsCiBuildIdFk < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  CONSTRAINT_NAME = 'fk_a325505e99'
+
+  def up
+    with_lock_retries do
+      remove_foreign_key_if_exists(:dast_site_profiles_builds, :ci_builds, name: CONSTRAINT_NAME)
+    end
+  end
+
+  def down
+    add_concurrent_foreign_key(:dast_site_profiles_builds, :ci_builds, column: :ci_build_id, on_delete: :cascade, name: CONSTRAINT_NAME)
+  end
+end

db/schema_migrations/20220110233155

+e7d9d79ffb8989ab39fe719217f22736244df70c2b1461ef5a1a3f1e74e43870
\ No newline at end of file

db/structure.sql

@@ -29562,9 +29562,6 @@ ALTER TABLE ONLY ci_builds
 ALTER TABLE ONLY ci_pipelines
     ADD CONSTRAINT fk_a23be95014 FOREIGN KEY (merge_request_id) REFERENCES merge_requests(id) ON DELETE CASCADE;
 
-ALTER TABLE ONLY dast_site_profiles_builds
-    ADD CONSTRAINT fk_a325505e99 FOREIGN KEY (ci_build_id) REFERENCES ci_builds(id) ON DELETE CASCADE;
-
 ALTER TABLE ONLY bulk_import_entities
     ADD CONSTRAINT fk_a44ff95be5 FOREIGN KEY (parent_id) REFERENCES bulk_import_entities(id) ON DELETE CASCADE;