[css-anchor-position] Specify when last remembered position options are forgotten. Remove issue.

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -1437,12 +1437,15 @@ laying out later elements cannot change this decision.
 	Layout does not "go backward", in other words.
 </div>
 
+At the time that {{ResizeObserver}} events are determined and delivered,
+if an element has a [=last successful position option=]
+but is not an [=absolutely positioned=] element,
+remove its [=last successful position option=].
+(This is intentionally identical to the treatment of [=last remembered sizes=].)
+
 Issue: Make sure the snapshotted scroll offset stuff is correct now,
 given interleaving.
 
-Issue: Add conditions for forgetting the [=last successful position option=],
-similar to the [=last remembered size=]
-
 Implementations may choose to impose an implementation-defined limit
 on the length of [=position options lists=],
 to limit the amount of excess layout work that may be required.