Provide valid C# example and remove C++/CLI function definition.

Author: AaronRobinsonMSFT

samples/snippets/csharp/VS_Snippets_CLR_System/system.runtime.interopservices.icustommarshaler/cs/source.cs

@@ -38,13 +38,27 @@ interface IUserData
 {
  void DoSomeStuff(
  [MarshalAs(UnmanagedType.CustomMarshaler,
- MarshalType="MyCompany.NewOldMarshaler")]
+ MarshalType="NewOldMarshaler")]
  INew pINew
  );
 }
 // </Snippet5>
 }
 
+// <Snippet6>
+public NewOldMarshaler : ICustomMarshaler
+{
+ public static ICustomMarshaler GetInstance(string pstrCookie)
+ => return new NewOldMarshaler();
+
+ public Object MarshalNativeToManaged( IntPtr pNativeData ) => throw new NotImplementedException();
+ public IntPtr MarshalManagedToNative( Object ManagedObj ) => throw new NotImplementedException();
+ public void CleanUpNativeData( IntPtr pNativeData ) => throw new NotImplementedException();
+ public void CleanUpManagedData( Object ManagedObj ) => throw new NotImplementedException();
+ public int GetNativeDataSize() => throw new NotImplementedException();
+}
+// </Snippet6>
+
 class StubClass
 {
  public static void Main() {}

xml/System.Runtime.InteropServices/ICustomMarshaler.xml

@@ -124,11 +124,9 @@ const IID IID_IOld = {0x9B2BAADD,0x0705,0x11D3,{0xA0,0xCD,0x00,0xC0,0x4F,0xA3,0x
  Returns the size of the unmanaged data to be marshaled. 
  
 ## Implementing the GetInstance Method 
- In addition to implementing the <xref:System.Runtime.InteropServices.ICustomMarshaler> interface, custom marshalers must implement a `static` method called `GetInstance` that accepts a <xref:System.String> as a parameter and has a return type of <xref:System.Runtime.InteropServices.ICustomMarshaler>. This `static` method is called by the common language runtime's COM interop layer to instantiate an instance of the custom marshaler. The string that is passed to `GetInstance` is a cookie that the method can use to customize the returned custom marshaler. 
+ In addition to implementing the <xref:System.Runtime.InteropServices.ICustomMarshaler> interface, custom marshalers must implement a `static` method called `GetInstance` that accepts a <xref:System.String> as a parameter and has a return type of <xref:System.Runtime.InteropServices.ICustomMarshaler>. This `static` method is called by the common language runtime's COM interop layer to instantiate an instance of the custom marshaler. The string that is passed to `GetInstance` is a cookie that the method can use to customize the returned custom marshaler. A minimal, but complete, <xref:System.Runtime.InteropServices.ICustomMarshaler> implementation in the form of the `NewOldMarshaler` type is below. 
  
-``` 
-static ICustomMarshaler *GetInstance(String *pstrCookie); 
-``` 
+ [!code-csharp[System.Runtime.InteropServices.ICustomMarshaler#6](~/samples/snippets/csharp/VS_Snippets_CLR_System/system.runtime.interopservices.icustommarshaler/cs/source.cs#6)]
  
 ## Applying MarshalAsAttribute 
  To use a custom marshaler, you must apply the <xref:System.Runtime.InteropServices.MarshalAsAttribute> attribute to the parameter or field that is being marshaled.