Remove unused stopwatch (#7878)

src/System.Management.Automation/engine/runtime/CompiledScriptBlock.cs

@@ -159,9 +159,10 @@ namespace System.Management.Automation
 
         private void ReallyCompile(bool optimize)
         {
+#if LEGACYTELEMETRY
             var sw = new Stopwatch();
             sw.Start();
-
+#endif
             if (!IsProductCode && SecuritySupport.IsProductBinary(((Ast)_ast).Extent.File))
             {
                 this.IsProductCode = true;