[evpp] Update to version 0.6.1

[zieckey]

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[msftclas]

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[ras0219-msft]

Thanks for the update PR!

I simplified the port to use vcpkg_from_github(), which also enables vcpkg install evpp --head to pull from the master branch.

I noticed some file(REMOVE) statements that were operating on non-existent directories, so I removed them. If you plan to export CMake config files in the future, please take a look at vcpkg_fixup_cmake_targets()[1] which might help quite a bit :).

[1] https://github.com/Microsoft/vcpkg/blob/master/scripts/cmake/vcpkg_fixup_cmake_targets.cmake

[zieckey]

@ras0219-msft Thanks for the refactoring.