Remove old .NET runtimes and SDKs
Remove old .NET runtimes and SDKs

- dotnet-sdk 3.1.412, 3.1.413, 3.1.414
- dotnet-sdk 5.0.400, 5.0.401, 5.0.402
- dotnet-runtime 3.1.18, 3.1.19, 3.1.20
- dotnet-runtime 5.0.9, 5.0.10, 5.0.11
- dotnet-aspnetcore 3.1.18, 3.1.19, 3.1.20
- dotnet-aspnetcore 5.0.9, 5.0.10, 5.0.11

Signed-off-by: Andrew Meyer <8896544cf29336d4c9052e18824ce3ac60d2aadc@vmware.com>

cloudfoundry-community/asp.net5-buildpack