prep for commands we'll be shipping as tools

add cleanup step to build, remove oob commands

only clean the sdk directory

Incorporate PR Feedback

scripts/dotnet-cli-build/Utils/FS.cs

@@ -34,6 +34,15 @@ namespace Microsoft.DotNet.Cli.Build
             }
         }
 
+        public static void RmFilesInDirRecursive(string dir, string filePattern)
+        {
+            var files = Directory.EnumerateFiles(dir, filePattern, SearchOption.AllDirectories);
+            foreach (var file in files)
+            {
+                FS.Rm(file);
+            }
+        }
+
         public static void Chmod(string file, string mode, bool recursive = false)
         {
             if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))