Blender Git Loki

Revert "Generate Xcode scheme files during configuration."

This reverts commit 5eb5978043c8e7036e15572e.

The change was problematic:
*Advanced users may prefer managing schemes manually and adding only
a few that they need, instead of one for every library/executable
Blender builds.

*If CMake creates schema files, it overwrites the changes a developer
made every time CMake is run. If Xcode creates scheme files, it keeps
settings/ environment variables intact.

If someone runs CMake very frequently, pass
`-DCMAKE_XCODE_GENERATE_SCHEME=ON` to `cmake` while configuring.