# Remove the submodule entry from .git/config
git submodule deinit -f path/to/submodule
# Remove the submodule directory from the superproject's .git/modules directory
rm -rf .git/modules/path/to/submodule
# Remove the entry in .gitmodules and remove the submodule directory located at path/to/submodule
git rm -f path/to/submodule