Remove unused files

***NO_CI***

CONTRIBUTING.md

@@ -1,3 +0,0 @@
-# Contributing to **nanoFramework**
-
-Please refer to the contribution guidelines at the Home repository [here](https://github.com/nanoframework/Home/blob/main/CONTRIBUTING.md).

config/SignClient.json

@@ -1,14 +0,0 @@
-{
-    "SignClient": {
-      "AzureAd": {
-        "AADInstance": "https://login.microsoftonline.com/",
-        "ClientId": "c248d68a-ba6f-4aa9-8a68-71fe872063f8",
-        "TenantId": "16076fdc-fcc1-4a15-b1ca-32c9a255900e"
-      },
-      "Service": {
-        "Url": "https://codesign.dotnetfoundation.org/",
-        "ResourceId": "https://SignService/3c30251f-36f3-490b-a955-520addb85001"
-      }
-    }
-  }
-