[clang] [llvm] [AArch64][SME] Remove SelectionDAG SME ABI lowering (PR #190950)

[Benjamin Maxwell via cfe-commits]

================
@@ -1,14 +0,0 @@
-; RUN: opt -S -mtriple=aarch64-linux-gnu -aarch64-sme-abi %s | FileCheck %s
----------------
MacDue wrote:

This file was testing emitting "aarch64_zt0_undef", which was a workaround I added for a previous issue with the selection dag lowering. I don't think there's any value in keeping the test now. 

https://github.com/llvm/llvm-project/pull/190950