Removed prebuilt shader headers and pdbs from project

[walbourn]

DirectX Tool Kit (both DX11 & DX12) has been including prebuilt shader headers and PDBs for many years. This adds a little bloat to the project, and sometimes some confusion, but it kept the built times down. It also made maintainece a pain.

A number of things have changed that are making me revisit this:

• FXC.EXE is very stable now and is no longer changing much. Therefore the need to keep 'workaround' versions of incs around is no longer a problem.

• My MSBuild skills have improved to the point where I can actually get it to behave the way I want w.r.t. to Windows 10 SDK versions and not impacting the Xbox variants.

• The NuGet package already solves the 'get working with a minimal of build time' problem since it includes the inc/pdbs built at the time of the release.

• For other variants of the library, I've been successfully using this model and have not gotten any feedback that developers find it frustrating.

• And finally, now that I've retired VS 2015 the odd-ball scenario of really old Windows SDKs is no longer a concern.

This PR also adds PreferredToolArchitecture=x64

[walbourn]

This removes about 10 MB from a 'clean' working directory.