chore(cleanup): remove redundant data-distance-service stub tests

- Covered by data-persistence-service tests (db/api).
- No references or compose entries.

services/data-distance-service/tests/db_tests.rs

@@ -1,6 +0,0 @@
-use data_persistence_service::{
-    db,
-    dtos::{CompanyProfileDto, DailyMarketDataDto, NewAnalysisResultDto, TimeSeriesFinancialDto},
-    models,
-};
-use sqlx::{postgres::PgPoolOptions, PgPool};