[definite-init] Remove dead code.

collectRetainCountInfo bails early if our memory instruction is a
mark_uninitialized... but our instruction is always a mark_uninitialized... so
this code is dead.

The origin of this code is from the flattening of the control flow in DI that
was necessary to be done to "extract" predictable mem opts from it.

rdar://40332620

Author: gottesmm

lib/SILOptimizer/Mandatory/DIMemoryUseCollectorOwnership.cpp

@@ -389,23 +389,6 @@ bool DIMemoryObjectInfo::isElementLetProperty(unsigned Element) const {
   return false;
 }
 
-void DIMemoryObjectInfo::collectRetainCountInfo(
-    DIElementUseInfo &OutVar) const {
-  if (isa<MarkUninitializedInst>(MemoryInst))
-    return;
-
-  // Collect information about the retain count result as well.
-  for (auto *Op : MemoryInst->getUses()) {
-    auto *User = Op->getUser();
-
-    // If this is a release or dealloc_stack, then remember it as such.
-    if (isa<StrongReleaseInst>(User) || isa<DeallocStackInst>(User) ||
-        isa<DeallocBoxInst>(User) || isa<DestroyValueInst>(User)) {
-      OutVar.trackDestroy(User);
-    }
-  }
-}
-
 //===----------------------------------------------------------------------===//
 //                        DIMemoryUse Implementation
 //===----------------------------------------------------------------------===//
@@ -535,7 +518,6 @@ class ElementUseCollector {
              "Should have been handled outside of here");
       // If this is a class pointer, we need to look through ref_element_addrs.
       collectClassSelfUses();
-      TheMemory.collectRetainCountInfo(UseInfo);
       return;
     }
 
@@ -544,8 +526,6 @@ class ElementUseCollector {
     } else {
       collectUses(TheMemory.getAddress(), 0);
     }
-
-    TheMemory.collectRetainCountInfo(UseInfo);
   }
 
   void trackUse(DIMemoryUse Use) { UseInfo.trackUse(Use); }
@@ -1794,14 +1774,12 @@ void swift::ownership::collectDIElementUsesFrom(
     assert(MemoryInfo.NumElements == 1 && "delegating inits only have 1 bit");
     auto *MUI = cast<MarkUninitializedInst>(MemoryInfo.MemoryInst);
     collectValueTypeDelegatingInitUses(MemoryInfo, UseInfo, MUI);
-    MemoryInfo.collectRetainCountInfo(UseInfo);
     return;
   }
 
   if (shouldPerformClassInitSelf(MemoryInfo)) {
     DelegatingClassInitElementUseCollector UseCollector(MemoryInfo, UseInfo);
     UseCollector.collectClassInitSelfUses();
-    MemoryInfo.collectRetainCountInfo(UseInfo);
     return;
   }
 

lib/SILOptimizer/Mandatory/DIMemoryUseCollectorOwnership.h

@@ -218,8 +218,6 @@ class DIMemoryObjectInfo {
 
   /// If the specified value is a 'let' property in an initializer, return true.
   bool isElementLetProperty(unsigned Element) const;
-
-  void collectRetainCountInfo(DIElementUseInfo &OutVar) const;
 };
 
 enum DIUseKind {