tempfile: update comment describing state transitions
Back when
1a9d15db25 (tempfile: a new module for handling temporary
files, 2015-08-10) added this comment, tempfile structs were held in
memory for the life of a process, and there were various guarantees
about which fields were valid in which states.
Since
422a21c6a0 (tempfile: remove deactivated list entries, 2017-09-05)
and
076aa2cbda (tempfile: auto-allocate tempfiles on heap, 2017-09-05),
the flow is quite different: objects come and go from the list, and
inactive ones are deallocated. And the previous commit removed the
"active" flag from the struct entirely.
Let's bring the comment up to date with the current code.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>