[feat] Add deleteTestCase and deleteTestSuite to XML-RPC API #1

Summary

The TestLink XML-RPC API (xmlrpc.class.php) is missing deleteTestCase and deleteTestSuite endpoints. Currently only deleteTestCaseSteps and deleteTestPlan exist.

Problem

MCP tool integrations (testlink-mcp) and other API clients cannot clean up test data programmatically. This causes:

• CI pipelines leave orphaned test cases and suites after each run
• No way to maintain a clean TestLink instance via automation
• delete_test_case in testlink-mcp has to fake deletion by marking status as obsolete (status 7), which is a workaround, not a real delete

Requested Endpoints

Context

• TestLink server: 1.9.20+
• API file: lib/api/xmlrpc/v1/xmlrpc.class.php
• Existing delete functions: deleteTestCaseSteps (line 6441), deleteTestPlan
• Reference: lib/testcases/containerEdit.php already has delete logic for the web UI

References

• testlink-mcp: dogkeeper886/testlink-mcp
• Discovered during CI cleanup: orphaned suites and test cases cannot be removed via API