Remove ios, windows8, and wp8 from Xamarin Forms PCL - nuget 3.0 opt-into error?

I'm working on a Xamarin Forms project. I want to target Android and Windows 10 UWP.

When I try to clean up the PCL by removing "Windows 8", "Windows Phone Silverlight 8", "Windows Phone 8.1", "Xamarin.ios", and "Xamarin.ios (classic)" from the PCL targets, I get the following nasty...

I'm really just trying to remove WP8 as I don't care about targeting it.

The project's targets cannot be changed. The selected targets require the project to opt-into NuGet 3.0 support, however, Visual Studio cannot automatically do this for you. Please uninstall all NuGet packages and try again.

How do you get a project to opt-into NuGet 3.0? Something else I should try?

environ: Xamarin Forms, VS2015

Thanks....

The solution that worked for me:

Uninstall Xamarin.Forms:

Right Click Solution -> Manage NuGet Packages -> Uninstall Xamarin.Forms -> Restart VS

Then remove build platforms:

Right Click Solution -> Properties -> Build -> under Targeting select Change -> Remove platform(s) -> Restart VS

Reinstall Xamarin.Forms:

Manage NuGet packages -> Search for Xamarin.Forms -> Install -> Restart VS

Another possible solution is to rename packages.config temporarily, change the PCL settings to the new target platforms, and then change the name of packages.config back again. This worked for me on my project using VS 2015. Can't take credit for this solution, read it on a blog some time back and just posting it here in case it helps someone. If I come across the blog article again I'll post the link here.