Revert "Set TargetFrameworkVersion to 2.3.3."

This reverts commit d2bb4d3b540cdfd1737560f62cde9600da3ff163.

On Windows, $(TargetFrameworkVersion)=v2.3 IS API-10; a v2.3.3 framework is
NOT installed, and not selectable, and selecting API-10 within e.g.
Visual Studio results in $(TargetFrameworkVersion)=v2.3, not v2.3.3.

Which is just a level of confusion I was not expecting...