Remove the cmake directory, previously imported as a Git submodule, in order to prepare have it embedded via Git Subtree.
Use subtree instead of submodule.
Squashed 'config/cmake/' content from commit 01a0da5

git-subtree-dir: config/cmake
git-subtree-split: 01a0da53c13897fc864fe96921bf957fa5e6dbca
Merge commit 'f2bc2468b569ffb62d0288d83e60829d50e840ef' as 'config/cmake'
Take into account change in the way the sub-directory is embedded.
Link to further articles on using Git Subtree.