Remove dead code that was not removed in PR #1255 (#1322)

Author: bergmeister

Rules/UseCorrectCasing.cs

@@ -32,11 +32,6 @@ public override IEnumerable<DiagnosticRecord> AnalyzeScript(Ast ast, string file
 
             IEnumerable<Ast> commandAsts = ast.FindAll(testAst => testAst is CommandAst, true);
 
-            bool isWindows = true;
-#if CORECLR
-            isWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
-#endif
-
             // Iterates all CommandAsts and check the command name.
             foreach (CommandAst commandAst in commandAsts)
             {