dotnet-svcutil doesn't unwrap certain method signatures

WSDL contracts with methods that return an array don't get "unwrapped" by dotnet-svcutil.

For example, a method with the following request/response wrappers:
```xml

```

Generates this interface method:
```c#
System.Threading.Tasks.Task updateFoosAsync(ServiceReference1.updateFoosRequest request);
```
Instead of unwrapping the request and response like this:
```c#
System.Threading.Tasks.Task updateFoosAsync(ServiceReference1.Foo[] foos);
```

Other methods are properly unwrapped. See attached example WSDL to reproduce:
[FooService.wsdl.txt](https://github.com/dotnet/wcf/files/1861393/FooService.wsdl.txt)