Revert "[Metadata] Preserve MD_prof when merging instructions when one is missing." (#134200)

Reverts #132433

I suspect this change caused a failure in the bolt build bot.
https://lab.llvm.org/buildbot/#/builders/113/builds/6621

```
!9185 = !{!"branch_weights", i32 3912, i32 802}
Wrong number of operands
!9185 = !{!"branch_weights", i32 3912, i32 802}
fatal error: error in backend: Broken module found, compilation aborted!
```

Author: snehasish

llvm/lib/Transforms/Utils/Local.cpp

@@ -3355,10 +3355,9 @@ static void combineMetadata(Instruction *K, const Instruction *J,
       case LLVMContext::MD_invariant_group:
         // Preserve !invariant.group in K.
         break;
-      // Keep empty cases for prof, mmra, memprof, and callsite to prevent them
-      // from being removed as unknown metadata. The actual merging is handled
+      // Keep empty cases for mmra, memprof, and callsite to prevent them from
+      // being removed as unknown metadata. The actual merging is handled
       // separately below.
-      case LLVMContext::MD_prof:
       case LLVMContext::MD_mmra:
       case LLVMContext::MD_memprof:
       case LLVMContext::MD_callsite:
@@ -3387,6 +3386,10 @@ static void combineMetadata(Instruction *K, const Instruction *J,
         if (!AAOnly)
           K->setMetadata(Kind, JMD);
         break;
+      case LLVMContext::MD_prof:
+        if (!AAOnly && DoesKMove)
+          K->setMetadata(Kind, MDNode::getMergedProfMetadata(KMD, JMD, K, J));
+        break;
       case LLVMContext::MD_noalias_addrspace:
         if (DoesKMove)
           K->setMetadata(Kind,
@@ -3433,16 +3436,6 @@ static void combineMetadata(Instruction *K, const Instruction *J,
     K->setMetadata(LLVMContext::MD_callsite,
                    MDNode::getMergedCallsiteMetadata(KCallSite, JCallSite));
   }
-
-  // Merge prof metadata.
-  // Handle separately to support cases where only one instruction has the
-  // metadata.
-  auto *JProf = J->getMetadata(LLVMContext::MD_prof);
-  auto *KProf = K->getMetadata(LLVMContext::MD_prof);
-  if (!AAOnly && (JProf || KProf)) {
-    K->setMetadata(LLVMContext::MD_prof,
-                   MDNode::getMergedProfMetadata(KProf, JProf, K, J));
-  }
 }
 
 void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,