remove choice of using aptitude instead of apt [dep #183]

this was an old hack to get around past issues with apt and is no longer necessary.

i deliberately left the configuration of aptitude in apt.conf.d stuff in place, since it's just a tiny thing and helps ensure aptitude works correctly if the user chooses to make use of it in interactive mode or whatever.

i have removed the ability for users to specify aptitude options as part of this. i've not bothered to try to automatically translate aptitude options to apt options for backwards compatibility since this would be rather difficult and messy. users using --aptitude-options will just have to adjust to --apt-options themselves.

Gbp-Dch: Short