UNINSTALL Onestepcheckout_Iosc
php -d memory_limit=2048M bin/magento module:uninstall Onestepcheckout_Iosc  --clear-static-content
run in mysql: DELETE FROM `core_config_data` WHERE `path` LIKE '%onestepcheckout_iosc/%';

If installed via composer:
rm -rf vendor/onestepcheckout

If installed manually:
rm -rf app/code/Onestepcheckout
UNINSTALL Idev_Iosc:
php -d memory_limit=2048M bin/magento module:uninstall Idev_Iosc  --clear-static-content
run in mysql: DELETE FROM `core_config_data` WHERE `path` LIKE '%idev_iosc/%';

If installed via composer:
rm -rf vendor/idev

If installed manually:
rm -rf app/code/Idev