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.

changes/ticket40137

+  o Minor features (state):
+    - When loading the state file, remove entries from the statefile that
+      have been obsolete for a long time.  Ordinarily Tor preserves
+      unrecognized entries in order to keep forward-compatibility, but
+      these statefile entries have not actually been used in any release
+      since before the 0.3.5.x. Closes ticket 40137.