Remove Spire.cpp.
Remove Spire.cpp.

This isn't used by the build any more, so this change removes it so that the `Spire/` subdirectory can (eventually) be a strict subset of the Spire github repository.

csyonghe/SpireMiniEngine,csyonghe/SpireMiniEngine,cherudim9/SpireMiniEngine,cherudim9/SpireMiniEngine