cmake: Drop Generate_Version_Info

[ChristianTackeGSI]

This is a small step towards #1076

But basically simplify the whole version generation code.

The git-version related stuff will come back quite soon.

For the external users of Generate_Version_Info this is a breaking change:

• If you just need to generate some files with your version number in it,
  use the standard configure_file CMake command.
• Alternatively consider creating a proper CMake Package with
  configure_package_config_file(), and write_basic_package_version_file().

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Checklist:

• Followed the Contributing Guidelines