[Windows] Remove VS Configurations

[CallumIddon]

jsoncpp wasn't added to the static library builds in VS and now they are both broken.

As Linux only supports outputting shared libraries I think should be reciprocate this on Windows with only dynamic libraries as the extra configurations just complicate things.

[stuartmorgan-g]

Reducing the number of configurations sounds good to me, especially at this stage where there's still a significant amount of churn.

[CallumIddon]

Also, would it be a good idea to have debug or release not both as we will have to add 2 more configurations when we add the GN builds to the example. And this would simplify the jsoncpp build process until we need both configurations.
The Linux implementations looks like it only supports one mode (I don't know which one) so until we start releasing prebuilt binaries I think we should just stick with one configuration.

[stuartmorgan-g]

I plan to add a simple Debug/Release switch to Linux shortly (and macOS already supports both configurations) so I prefer to keep both for Windows. Particularly since in the example app, debug mode actually changes the Dart behavior.

I'm fine with only adding GN as an option for Debug in the example VS project for now though, since the GN builds are still experimental.

[stuartmorgan-g]

Reopening since the broken static library build options still need to be removed.

[CallumIddon]

@stuartmorgan Can you add this to In Progress in the Overview Kanban due to #209.

[stuartmorgan-g]

I'm not really tracking status live on the Kanban board; I'll generally be updating it once or twice a week. So things like this where the time between someone starting work and the patch landing is very short will jump straight to Done, which is fine.