[lldb][NFCI] Remove unneeded ConstString from ValueObject::GetValueForExpressionPath_Impl

lldb/source/Core/ValueObject.cpp

case '.': // or fallthrough from ->
         *reason_to_stop =
             ValueObject::eExpressionPathScanEndReasonDotInsteadOfArrow;
         *final_result = ValueObject::eExpressionPathEndResultTypeInvalid;
         return nullptr;
       }
       temp_expression = temp_expression.drop_front(); // skip . or >
 
       size_t next_sep_pos = temp_expression.find_first_of("-.[", 1);
-      ConstString child_name;
       if (next_sep_pos == llvm::StringRef::npos) // if no other separator just
                                                  // expand this last layer
       {
-        child_name.SetString(temp_expression);
+        llvm::StringRef child_name = temp_expression;
         ValueObjectSP child_valobj_sp =
             root->GetChildMemberWithName(child_name);
 
         if (child_valobj_sp.get()) // we know we are done, so just return
         {
           *reason_to_stop =
               ValueObject::eExpressionPathScanEndReasonEndOfString;
           *final_result = ValueObject::eExpressionPathEndResultTypePlain;
case '.': // or fallthrough from ->
           *reason_to_stop =
               ValueObject::eExpressionPathScanEndReasonNoSuchChild;
           *final_result = ValueObject::eExpressionPathEndResultTypeInvalid;
           return nullptr;
         }
       } else // other layers do expand
       {
         llvm::StringRef next_separator = temp_expression.substr(next_sep_pos);
-
-        child_name.SetString(temp_expression.slice(0, next_sep_pos));
+        llvm::StringRef child_name = temp_expression.slice(0, next_sep_pos);
 
         ValueObjectSP child_valobj_sp =
             root->GetChildMemberWithName(child_name);
         if (child_valobj_sp.get()) // store the new root and move on
         {
           root = child_valobj_sp;
           remainder = next_separator;
           *final_result = ValueObject::eExpressionPathEndResultTypePlain;