ubuntu-minimal: Remove dependency on ureadahead

ubuntu-minimal should not depend on ureadahead.

Reason #1, on theoretical grounds: ubuntu-minimal is supposed to pull in the minimal functioning system. ureadahead is not required for a functioning system. Therefore, ubuntu-minimal should not depend on ureadahead.

Reason #2, on practical grounds: ureadahead does have some drawbacks (such as not working and causing error messages when /var is on a separate partition, or actually increasing boot time), and on servers, which are rarely rebooted, it's not of much use anyway. Therefore, I (and presumably others) would prefer to remove it, but this requires removing ubuntu-minimal as well, which the latter's package description recommends against. Removing the dependency would allow for a clean removal of readahead while keeping ubuntu-minimal.

Please note that I'm not opposed to ureadhead per se – I do recognize that it's likely to be beneficial to the majority of systems, and I'm fine with having it installed by default; I just want to be able to uninstall it without affecting other packages.

Perhaps instead of having a hard dependency, ubuntu-minimal could recommend or suggest ureadahead? Or maybe the dependency should be moved to ubuntu-desktop (or some related package), since desktop systems are most likely to benefit from it, and probably also most likely to have /var on the root partition.

For the record, I'm running Ubuntu 10.04.4 LTS, but according to http://packages.ubuntu.com/raring/ubuntu-minimal, the dependency still exists in raring.