[llvm] [RISCV][NFC] Remove unused getSelectionDAGInfo (PR #98172)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> The RISCVSubtarget creates an instance of `SelectionDAGTargetInfo`

I don't see where this occurs. I don't think it is ever created.

https://github.com/llvm/llvm-project/pull/98172