Run in terminal
git rm <path-to-submodule>
rm -rf .git/modules/<path-to-submodule>
git config --remove-section submodule.<path-to-submodule>
Example:
- Open terminal
cd /Users/You/Documents/Github/MySaucyProject
git rm ./lib/SubmoduleThatIDespise
rm -rf .git/modules/lib/SubmoduleThatIDespise
git config --remove-section submodule.lib/SubmoduleThatIDespise