[llvm] [AMDGPU] Partially revert my llvm::less_second patch (PR #136615)

[Jakub Kuderski via llvm-commits]

================
@@ -589,7 +589,7 @@ void PipelineSolver::populateReadyList(
   }
 
   if (UseCostHeur)
-    llvm::sort(ReadyList, llvm::less_second());
+    std::sort(ReadyList.begin(), ReadyList.end(), llvm::less_second());
----------------
kuhar wrote:

I think it's fine as is as we investigate 

https://github.com/llvm/llvm-project/pull/136615