- Removes special `DeleteSavepoint` and uses the existing cursor restoration
mechanism.
- This required some restructuring of `DeleteState` to avoid cloning it, i.e.
some negotations with the borrow checker.
- CursorContext now takes a SeekOp as well to allow retaining the behavior
that we use LT for seeking after a delete-induced rebalancing. This behavior
will probably be removed as part of fixing #2004, but here I am trying to
preserve the current semantics.
50fd7ec58b