[tests] Fix a couple of registrar tests to work on device.

[rolfbjarne]

Fixes the following test failures:

[FAIL] BlockSignatureTest.WithoutUserDelegateTypeAttribute : System.ExecutionEngineException : Attempting to JIT compile method '(wrapper native-to-managed) MonoTouchFixtures.ObjCRuntime.BlockSignatureTest:<WithoutUserDelegateTypeAttribute>m__0 (intptr,intptr)' while running with --aot-only. See http://docs.xamarin.com/ios/about/limitations for more information.
      at (wrapper managed-to-native) System.Runtime.InteropServices.Marshal:GetFunctionPointerForDelegateInternal (System.Delegate)
      at System.Runtime.InteropServices.Marshal.GetFunctionPointerForDelegate (System.Delegate d) [0x00011] in /work/maccore/xcode8/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Runtime.InteropServices/Marshal.cs:1714
      at ObjCRuntime.BlockLiteral.SetupBlock (System.Delegate trampoline, System.Delegate userDelegate) [0x0000b] in /work/maccore/xcode8/xamarin-macios/src/ObjCRuntime/Blocks.cs:92
      at MonoTouchFixtures.ObjCRuntime.BlockSignatureTest.WithoutUserDelegateTypeAttribute () [0x00049] in /work/maccore/xcode8/xamarin-macios/tests/monotouch-test/ObjCRuntime/RegistrarTest.cs:2585
      at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
      at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in /work/maccore/xcode8/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:309

[FAIL] BlockSignatureTest.WithUserDelegateTypeAttribute : System.ExecutionEngineException : Attempting to JIT compile method '(wrapper native-to-managed) MonoTouchFixtures.ObjCRuntime.BlockSignatureTest:<WithUserDelegateTypeAttribute>m__2 (intptr,intptr)' while running with --aot-only. See http://docs.xamarin.com/ios/about/limitations for more information.
      at (wrapper managed-to-native) System.Runtime.InteropServices.Marshal:GetFunctionPointerForDelegateInternal (System.Delegate)
      at System.Runtime.InteropServices.Marshal.GetFunctionPointerForDelegate (System.Delegate d) [0x00011] in /work/maccore/xcode8/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Runtime.InteropServices/Marshal.cs:1714
      at ObjCRuntime.BlockLiteral.SetupBlock (System.Delegate trampoline, System.Delegate userDelegate) [0x0000b] in /work/maccore/xcode8/xamarin-macios/src/ObjCRuntime/Blocks.cs:92
      at MonoTouchFixtures.ObjCRuntime.BlockSignatureTest.WithUserDelegateTypeAttribute () [0x00049] in /work/maccore/xcode8/xamarin-macios/tests/monotouch-test/ObjCRuntime/RegistrarTest.cs:2596
      at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
      at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in /work/maccore/xcode8/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:309

[monojenkins]

Build success