🐛(backend) fix flaky test with search contact

Sometimes emails generated by faker in data field match search.
So it's necessary to create contacts with empty data field
to search contacts by full_name in tests.

src/backend/core/api/client/viewsets.py

@@ -25,8 +25,6 @@ from core.api import permissions
 from core.api.client import serializers
 from core.utils.raw_sql import gen_sql_filter_json_array
 
-SIMILARITY_THRESHOLD = 0.04
-
 
 class NestedGenericViewSet(viewsets.GenericViewSet):
     """