Fix bug introduced in rev 1.236 (April-3-2014):

Areafix requests to unlink a node from an area would corrupt the list of
linked nodes: the *last* listed node would always be removed. If this was
not the node that submitted the areafix request, then 2 nodes would be
removed from the list of linked-nodes for an echo.
To simplify this, we're just going to not write the removed node back to
the area file, but leave it in the in-memory list. So technically, the node
won't be unlinked until the next run of SBBSecho when the area file is
re-parsed. If that's a problem, we can always add run-time removal from
the in-memory list later. Reported by Alterego (ALTERANT).