Remove haveged

haveged was added 8 years ago to increase entropy (and prevent entropy starvation I assume).

A lot has changed since, most notable:

• /dev/random no longer blocks after CRNG initialization (since v5.6, LWN article)
• random: try to actively add entropy rather than passively wait for it (since 5.4, merge commit with more reasoning, LKML discussion)

See also: https://systemd.io/RANDOM_SEEDS/

Note: I'm not a expert on this subject, but from what I understand it should be safe to remove haveged.