dagop: use fctx.rev() consistently in filectxancestors()

We can't use fctx.linkrev() to sort fctxs coming from multiple files.
This was changed at 24b57c3899f8 due to performance issue, but we know
we evaluate parent.rev() in revset anyway.

mercurial/dagop.py

@@ -87,7 +87,7 b' def filectxancestors(fctx, followfirst=F'
     yield c
     while True:
         for parent in c.parents()[:cut]:
-            visit[(parent.linkrev(), parent.filenode())] = parent
+            visit[(parent.rev(), parent.filenode())] = parent
         if not visit:
             break
         c = visit.pop(max(visit))