layers: Fix thread-safety fails in OT FreeXxx APIs
layers: Fix thread-safety fails in OT FreeXxx APIs

Tracking data was cleaned up after calling down the chain in
FreeCommandBuffers and FreeDescriptorSets -- this left a hole that
another thread could walk through and corrupt the tracking data.

Change-Id: I7cc9c9bfae9f1ea179122125dd09952650f14d81

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools