Remove redundant `HomeserverTestCase.render`

tests/federation/test_complexity.py

tests/federation/test_federation_server.py

tests/federation/transport/test_server.py

tests/handlers/test_directory.py

tests/handlers/test_message.py

tests/handlers/test_typing.py

tests/handlers/test_user_directory.py

tests/rest/admin/test_admin.py

tests/rest/admin/test_device.py

tests/rest/admin/test_event_reports.py

tests/rest/admin/test_media.py

tests/rest/admin/test_room.py

tests/rest/admin/test_statistics.py

tests/rest/admin/test_user.py

tests/rest/client/test_ephemeral_message.py

tests/rest/client/test_identity.py

tests/rest/client/test_redactions.py

tests/rest/client/test_retention.py

tests/rest/client/test_shadow_banned.py

tests/rest/client/test_third_party_rules.py