Remove username password integration test

[RyAuld]

Summary
Removes username/password integration tests that use the deprecated Resource Owner Password Credentials (ROPC) flow.

Rationale

• Deprecated API: The username/password authentication flow tested in this file uses ROPC, which is deprecated and not recommended for production use
• Security Concerns: Deliberate test failures followed by successes may trigger Azure AD's spray attack detection, potentially marking test users as risky and generating security alerts
• Build Reliability: These tests have been causing intermittent build failures due to authentication timing issues and account lockout policies
• Impact
• Improves build stability by removing flaky tests
• Eliminates potential security alert noise from test authentication patterns
• No loss of critical functionality testing since ROPC is deprecated
• Files Changed

❌ Removed: UsernamePasswordIntegrationTests.NetFwk.cs

[trwalke]

verify if CCA scenario is needed.