rename is_detached_from_{original_,}ancestor (just the rename)

pageserver/src/tenant/remote_timeline_client/index.rs

@@ -236,9 +236,8 @@ impl Lineage {
             .is_some_and(|(_, ancestor_lsn, _)| ancestor_lsn == lsn)
     }
 
-    // FIXME: rename to is_detached_from_ancestor as the reparented will not be detached from
-    // original ancestor
-    pub(crate) fn is_detached_from_original_ancestor(&self) -> bool {
+    /// Returns true if the timeline originally had an ancestor, and no longer has one.
+    pub(crate) fn is_detached_from_ancestor(&self) -> bool {
         self.original_ancestor.is_some()
     }