Remove distinct in import_issues_count

We make a call to `uniq` later on in the method so there's no need to
select on distinct entries here, which should slightly improve the
performance of the query, the downside being an increase in memory
usage.

Jira-Issue: MAV-2001

Author: thomasleese

app/helpers/imports_helper.rb

@@ -14,9 +14,7 @@ module ImportsHelper
 
   def import_issues_count
     vaccination_records_with_issues =
-      policy_scope(VaccinationRecord).with_pending_changes.distinct.pluck(
-        :patient_id
-      )
+      policy_scope(VaccinationRecord).with_pending_changes.pluck(:patient_id)
 
     patients_with_issues = policy_scope(Patient).with_pending_changes.pluck(:id)