[llvm] [DirectX] Strip `dx.rootsignatures` metadata during `dxil-prepare` (PR #145746)

[via llvm-commits]

================
@@ -33,13 +33,13 @@
 ; CHECK-NEXT:   DXIL Translate Metadata
 ; CHECK-NEXT:   DXIL Post Optimization Validation
 ; CHECK-NEXT:   DXIL Op Lowering
+; CHECK-NEXT: DXIL Root Signature Analysis
----------------
joaosaffran wrote:

```suggestion
; CHECK-NEXT:   DXIL Root Signature Analysis
```

https://github.com/llvm/llvm-project/pull/145746