If you need to stop tracking a lot of ignored files, you can combine some commands:
git ls-files -i --exclude-standard | xargs -L1 git rm --cached
This would stop tracking the ignored files. If you want to actually remove files from filesystem, do not use the --cached option. You can also specify a folder to limit the search, such as:
git ls-files -i --exclude-standard -- ${FOLDER} | xargs -L1 git rm