Fix netfx build break in Microsoft.Diagnostics.Tracing.EventSource.Redist

Author: stephentoub

src/Common/src/CoreLib/System/Diagnostics/Tracing/StubEnvironment.cs

@@ -6,6 +6,9 @@
 using System.Collections.Generic;
 
 #if ES_BUILD_STANDALONE
+using System.Runtime.InteropServices;
+using System.Security;
+
 namespace Microsoft.Diagnostics.Tracing.Internal
 #else
 namespace System.Diagnostics.Tracing.Internal
@@ -327,9 +330,6 @@ public static bool ReflectionOnly(this Assembly assm)
 #if ES_BUILD_STANDALONE
 internal static partial class Interop
 {
-    using System.Runtime.InteropServices;
-    using System.Security;
-
     [SuppressUnmanagedCodeSecurityAttribute()]
     internal static partial class Kernel32
     {