[llvm] [CodeGen] Remove `applySplitCriticalEdges` in `MachineDominatorTree` (PR #97055)

[Quentin Colombet via llvm-commits]

qcolombet wrote:

> Remove MachineDominatorTree update code in MachineBasicBlock::SplitCriticalEdge.

Could we instead have the MachineBasicBlock use the `MDTU`?

Having each user of "split critical edge" replicate the call to MDTU doesn't sound like a great trade-off to me.

Other than that, +1 on removing the custom update logic and using the more standard one.

https://github.com/llvm/llvm-project/pull/97055