Revert "Merge branch 'feature/modern-cmake-documentation-generator' into 'master'"

This reverts merge request !1020 (merged)

Due to conflicts with the pyproject.toml dependency list, we have to think about this again.

cmake/scripts/conf.py.in

@@ -2,7 +2,7 @@ import sys
 
 sys.path.append('@DUNE_SPHINX_EXT_PATH@')
 
-extensions = ['sphinx_cmake_dune','sphinxcontrib.moderncmakedomain']
+extensions = ['sphinx_cmake_dune']
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.