The enabledLayerCount member of VkApplicationInfo is automatically populated by setting ppEnabledLayerNames. This is a feature of the LWJGL bindings, similar to auto-sized parameters in functions. If you'd like to set it to 0, pass null to ppEnabledLayerNames.
If you'd like to set it directly for some reason, you can use the unsafe accessor (VkApplicationInfo.nenabledLayerCount).