[DXIL] Remove extraneous include from DXILABI.h (#100620)

I'm not sure how an include of StringSwitch got here, but it isn't
needed.

llvm/include/llvm/Frontend/HLSL/HLSLResource.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_FRONTEND_HLSL_HLSLRESOURCE_H
 #define LLVM_FRONTEND_HLSL_HLSLRESOURCE_H
 
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DXILABI.h"
 
 namespace llvm {

llvm/include/llvm/Support/DXILABI.h

@@ -17,7 +17,7 @@
 #ifndef LLVM_SUPPORT_DXILABI_H
 #define LLVM_SUPPORT_DXILABI_H
 
-#include "llvm/ADT/StringSwitch.h"
+#include <cstdint>
 
 namespace llvm {
 namespace dxil {