[lldb-vscode] Avoid a -Wunused-but-set-variable warning. NFC.

[labath]

I think this qualifies as an obvious fix.

lldb/tools/lldb-vscode/lldb-vscode.cpp

if (portno != -1) {
     } else {
       return EXIT_FAILURE;
     }
   } else {
     g_vsc.input.descriptor = StreamDescriptor::from_file(fileno(stdin), false);
     g_vsc.output.descriptor = StreamDescriptor::from_file(new_stdout_fd, false);
   }
 
-  uint32_t packet_idx = 0;
   while (!g_vsc.sent_terminated_event) {
     llvm::json::Object object;
     lldb_vscode::PacketStatus status = g_vsc.GetNextObject(object);
     if (status == lldb_vscode::PacketStatus::EndOfFile)
       break;
     if (status != lldb_vscode::PacketStatus::Success)
       return 1; // Fatal error
 
     if (!g_vsc.HandleObject(object))
       return 1;
-    ++packet_idx;
   }
 
   return EXIT_SUCCESS;
 }