Enable some of the unnecessary code rules (#799)

* CA1823 Avoid unused private fields
* CA1847 Use string.Contains(char) instead of string.Contains(string) with single characters
* IDE0005 Remove unnecessary import
* IDE0051 Private member is unused
* IDE0052 Private member is unread

src/LibKubernetesGenerator/KubernetesClientSourceGenerator.cs

@@ -4,7 +4,6 @@ using NSwag;
 using Nustache.Core;
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.Linq;
 using System.Reflection;