.NET Core 2.0 reached EOL last year. This removes multi-targeting our test projects and test assets to only use .NET Core 2.1 and .NET Framework 4.6.1.
Changes:
* Stop producing Microsoft.AspNetCore.Routing.DecisionTree.Sources. I could not find any usages outside of the Microsoft.AspNetCore.Routing assembly, so I've moved this to be a subfolder of code in the Microsoft.AspNetCore.Routing project.
* Stop building src/Routing as a submodule. Use ProjectReference instead
* Move projects from src/Routing into src/Http/Routing/ and src/Http/Routing.Abstractions/
* Update package baselines and dependencies to support building routing projects and samples
Nate McMaster