Remove redundant user re-link branch in CSV importer

update_or_create already persists member.user via defaults, so the
follow-up `if create_account and member.user_id is None` block was
unreachable dead code. Removing it brings importer coverage to 100%
with no behavior change (existing link-existing-user test still passes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

members/services/member_csv_importer.py

@@ -127,10 +127,6 @@ class MemberCsvImporter:
             },
         )
 
-        if create_account and member.user_id is None:
-            member.user = user
-            member.save(update_fields=["user"])
-
         club, club_created = Club.objects.get_or_create(name=club_name)
 
         _, membership_created = ClubMembership.objects.update_or_create(