Net462update

[geckogeckogecko]

As .NET 4.6.1 is no longer supported, the changes made update the project to .NET 4.6.2, and remove other references to outdated .NETCore versions.
Further reading here: https://devblogs.microsoft.com/dotnet/net-framework-4-5-2-4-6-4-6-1-will-reach-end-of-support-on-april-26-2022/

[Pilchard123]

For reference, I have a similar PR at #4221 . I added the reference assemblies there rather than removing net461/netcoreapp2.1/net5.0 because according to #2181 dropping support for those is being considered as part of v14, and I think v13 is still the current one.

[lahma]

#4001 has the big cleanup

[RicoSuter]

Already done in the v14 PR.