Remove legacy Spring XML configuration files

Remove obsolete configuration files replaced by Spring Boot 3.5:
- Legacy XML-based test context configuration
- Legacy database property files (HSQL/MySQL)
- Legacy log4j.properties (replaced by Logback)
- Legacy populateDB.sql (replaced by Flyway migrations)

These files are no longer needed with modern Spring Boot configuration
and TestContainers-based testing approach.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: dfcoffin