Revert "[.gitmodules] add submodule url for dune-common, dune-grid, dune-geometry"
Revert "[.gitmodules] add submodule url for dune-common, dune-grid, dune-geometry"

This reverts commit d290c2979e79edd5dc0cb6862e614db39d7d9a77.

dune-community/dune-gdt-super