Simplify InternalsVisibleTo

If the $(PublicKey) property is used, the SDK targets will automatically use it for the assembly attributes.

See dotnet/sdk#3439

Simplifies spectreconsole/spectre.console#1623

Author: kzu

src/Spectre.Console.Cli/Spectre.Console.Cli.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup Label="REMOVE THIS">
-    <InternalsVisibleTo Include="Spectre.Console.Cli.Tests, PublicKey=$(SnkPublicKey)" />
+    <InternalsVisibleTo Include="Spectre.Console.Cli.Tests" />
   </ItemGroup>
 
   <ItemGroup>