[llvm] [InstrRef][nfc] Remove usage of unique_ptrs of arrays (PR #74203)

[Felipe de Azevedo Piovezan via llvm-commits]

felipepiovezan wrote:

I'll go ahead and merge this, but happy to address the reserve issue afterwards if you disagree with my assessment from above.

https://github.com/llvm/llvm-project/pull/74203