[llvm] [delinearize] clear Subscripts and Sizes vectors (NFC) (PR #156495)

[Sjoerd Meijer via llvm-commits]

https://github.com/sjoerdmeijer approved this pull request.

Reverse ping, @sebpop. 
Would be good to get this out of the way if it is still useful. 

https://github.com/llvm/llvm-project/pull/156495