Remove dupe ropc b2c tests

[gladjohn]

Fixes - dupe tests

Changes proposed in this request
This pull request removes the B2CUsernamePasswordIntegrationTests.cs test file and moves its main test logic into the UsernamePasswordIntegrationTests.NetFwk.cs file. The migration ensures that B2C ROPC authentication scenarios continue to be tested as part of the .NET Framework integration tests. The most important changes are grouped below.

Test File Removal and Migration

• Deleted the entire B2CUsernamePasswordIntegrationTests.cs file, including its B2C ROPC test logic.
• Migrated the B2C ROPC account validation logic—such as claims checks and account assertions—into the RunB2CHappyPathTestAsync method in UsernamePasswordIntegrationTests.NetFwk.cs. This preserves the coverage of B2C authentication scenarios in the integration test suite.

Testing
tests

Performance impact
n/a

Documentation

• All relevant documentation is updated.