Bug#864285: man page of apt incomplete, missing "clean" subcommand

["L.Schmidt" <l@scarydevilmonastery.net>]

Since apt runs here on mass storage starved small single board
computers, I do indeed consider `clean' one of the important apt
subcommands, as in "most used", yes. I disagree with the notion that
documentation incompleteness and referral to other documents is
preferrable to "distraction" by information. After all, one peruses a
man page for obtaining information, not for minimising distraction.

But the man page flaw is, IMHO, not the lack of complete documention
of `clean' functionality. Instead it is that it's not evident from
the man page that this subcommand is understood and executed. There
may be other supported subcommands, about which I don't know from
reading the man page alone - instead I may have to trial and error
potential candidates (or look for other sources of information).