[WCF] Make BasicHttpBinding.AllowCookies work

This patch is from Brendan Zagaeski and fixes bug 11307

The description of the problem was:

In Mono 2.10.12, the BasicHttpBinding property no longer supports
EnableHttpCookieContainer because it is Depreciated. The replacement
is AllowCookies, but this property does not work. Upon inspection of
the source source, we find that the HttpCookieContainerBindingElement
is added in accordance with EnableHttpCookieContainer, but not
AllowCookies.

The conditional compile logic at [1] is no longer needed for
Xamarin.iOS or Xamarin.Android.