THIRD-PARTY-NOTICES.txt file contains test-only notices

[NikolaMilosavljevic]

Test-only notices should not be included in the main repo's TPN file: https://github.com/dotnet/winforms/blob/main/THIRD-PARTY-NOTICES.TXT

Please remove this notice and include it alongside tests that need it. See this as an example: https://github.com/dotnet/runtime/blob/main/src/tests/JIT/Performance/CodeQuality/Burgers/THIRD-PARTY-NOTICES

This issue was uncovered while updating TPN file for .NET 8 release: dotnet/runtime#91933 The process assembles notices from all repos into a shared TPN file that ships with SDK.

[John-Qiao]

Verified it in the main branch of Winforms repo for .Net 9.0, the content of THIRD-PARTY-NOTICES.TXT is changed to below: