использовать команду ниже, опция удаления пула эквивалентна очистке
sudo apt-get --purge remove gcc-4.9
согласно apt-get руководству:
--purge
Use purge instead of remove for anything that would be removed. An
asterisk ("*") will be displayed next to packages which are
scheduled to be purged. remove --purge is equivalent to the purge
command. Configuration Item: APT::Get::Purge.