[llvm] [CycleInfo] Remove GenericCycle::TopLevelCycle. NFC (PR #209677)

[Alexis Engelke via llvm-commits]

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@@ -311,9 +308,6 @@ void GenericCycleInfo<ContextT>::moveTopLevelCycleToNewParent(CycleT *NewParent,
   *Pos = std::move(CurrentContainer.back());
   CurrentContainer.pop_back();
   Child->ParentCycle = NewParent;
-  Child->TopLevelCycle = NewParent;
-  for (CycleT *Cycle : depth_first(Child))
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aengelke wrote:

Maybe we should at some point drop GraphTraits for Cycle to prevent accidental use of these inefficient iterators?

https://github.com/llvm/llvm-project/pull/209677