[clang] [clang][SME] Remove folding of `__arm_in_streaming_mode()` (NFC) (PR #150917)

[Gaëtan Bossu via cfe-commits]

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

I've looked at the existing clang and InstCombine tests; the change looks good to me.

https://github.com/llvm/llvm-project/pull/150917