Update diagnostics repo to latest arcade

[mikem8361]

Remove changes to the command build.ps1 for architecture. This will allow arcade to be updated with DARC. It will require installing the x86 SDK and runtimes for testing into a separate directory.

[mikem8361]

• Test 3.1 runtime channel
• Remove testing 1.1.
• Use the "latest" channels for 2.1, 2.2, 3.0, etc. instead of hard coding.

[tommcdon]

Moving to 5.0 as we do not need to update arcade to test 2.1, 3.1 and remove 1.1. #606