[dotnet-linker] Delete unnecessary NuGet.config. (#10466)

tools/dotnet-linker/NuGet.config

@@ -1,13 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<configuration>
-	<config>
-		<add key="repositorypath" value="packages" />
-		<add key="globalPackagesFolder" value="packages" />
-	</config>
-	<packageSources>
-		<add key="Nuget Official" value="https://www.nuget.org/api/v2/" />
-		<add key="Dotnet arcade" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" />
-		<add key="dotnet5" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json" />
-	</packageSources>
-</configuration>
-