[test] Disable a test for XI (only) as it does not support dynamic proxy code generation
There's no need for those special NET_2_1 cases (excluding System.Char) anymore and it fixes 6 S.SM.W unit tests failures for XI.
There's no need for those special NET_2_1 cases (not using NameValueCollection like MS) anymore and it fixes 7 S.SM.W unit tests failures for XI (e.g. case sensitiveness)
The mobile profile can support IBindingRuntimePreferences on WebHttpBinding. Fix one S.SM.W unit test failure for XI