Remove long-obsolete members from the state file.

Tor has a feature to preserve unrecognized state file entries in order to maintain forward compatibility. But this feature, along with some unused code that we never actually removed, led to us keeping items that were of no use to the user, other than at worst to preserve ancient information about them.

This commit adds a feature to remove obsolete entries when we load the file.

Closes ticket 40137.

Github CI at https://github.com/torproject/tor/pull/2085

Closes #40137 (closed)

mentioned in issue #40137 (closed)

assigned to @asn

LGTM! Merged!

closed