revert contributing

Author: TheAngryByrd

CONTRIBUTING.md

@@ -2,30 +2,8 @@
 
 1. Clone repo.
 2. Install local tools with `dotnet tool restore`
-
-## Testing
-
-Testing against different .NET runtimes is a bit of a chore because we want to let the runtime load the current runtime's Microsoft.Build assemblies. Unfortunately, we can't have the `global.json` set to `net9.0` because the `Microsoft.Build` assemblies are compatible with the .NET 9 runtime, and will try to load them, even in a net8.0 TFM context. (Chet to fill in longer description as to why.)
-
-### Against LTS (net8.0)
-1. Run tests with `dotnet run --project .\build\ -- -t Test`
-    1. This should chose the `Test:net9.0` target and run against that runtime
-
-
-### Against STS (net9.0)
-1. Change global.json to use net9.0
-    ```json
-        "sdk": {
-            "version": "9.0.100",
-            "rollForward": "latestMinor",
-            "allowPrerelease": true
-        }
-    ```
-2. Set environment variable `BuildNet9` to `true`
-    1. Bash: `export BuildNet9=true`
-    2. PowerShell: `$env:BuildNet9 = "true"`
 3. Run tests with `dotnet run --project .\build\ -- -t Test`
-    1. This should chose the `Test:net9.0` target and run against that runtime
+4. Create packages with `dotnet run --project .\build\ -- -t Pack`
 
 ## Release