layers: Add getSamplerNode() helper

Kill sampler_map_ in DescriptorSet and add getSamplerNode() helper
and use it instead.
diff --git a/layers/descriptor_sets.h b/layers/descriptor_sets.h
index fcb409c..eddbff3 100644
--- a/layers/descriptor_sets.h
+++ b/layers/descriptor_sets.h
@@ -160,7 +160,7 @@
 };
 // Shared helper functions - These are useful because the shared sampler image descriptor type
 //  performs common functions with both sampler and image descriptors so they can share their common functions
-bool ValidateSampler(const VkSampler, const std::unordered_map<VkSampler, std::unique_ptr<SAMPLER_NODE>> *);
+bool ValidateSampler(const VkSampler, const core_validation::layer_data *);
 bool ValidateImageUpdate(VkImageView, VkImageLayout, VkDescriptorType,
                          const std::unordered_map<VkImageView, VkImageViewCreateInfo> *,
                          const std::unordered_map<VkImage, IMAGE_NODE> *, const std::unordered_map<VkImage, VkSwapchainKHR> *,
@@ -269,7 +269,6 @@
                                    std::unordered_map<VkDescriptorSet, cvdescriptorset::DescriptorSet *> *,
                                    const core_validation::layer_data *,
                                    const std::unordered_map<VkDescriptorSetLayout, cvdescriptorset::DescriptorSetLayout *> &,
-                                   const std::unordered_map<VkSampler, std::unique_ptr<SAMPLER_NODE>> &,
                                    const std::unordered_map<VkImageView, VkImageViewCreateInfo> &,
                                    const std::unordered_map<VkImage, IMAGE_NODE> &,
                                    const std::unordered_map<VkImage, VkSwapchainKHR> &,
@@ -297,7 +296,6 @@
   public:
     using BASE_NODE::in_use;
     DescriptorSet(const VkDescriptorSet, const DescriptorSetLayout *, const core_validation::layer_data *,
-                  const std::unordered_map<VkSampler, std::unique_ptr<SAMPLER_NODE>> *,
                   const std::unordered_map<VkImageView, VkImageViewCreateInfo> *, const std::unordered_map<VkImage, IMAGE_NODE> *,
                   const std::unordered_map<VkImage, VkSwapchainKHR> *,
                   const std::unordered_map<VkSwapchainKHR, SWAPCHAIN_NODE *> *);
@@ -377,8 +375,6 @@
     std::vector<std::unique_ptr<Descriptor>> descriptors_;
     // Ptrs to object containers to verify bound data
     const core_validation::layer_data *device_data_;
-    const std::unordered_map<VkBufferView, VkBufferViewCreateInfo> *buffer_view_map_;
-    const std::unordered_map<VkSampler, std::unique_ptr<SAMPLER_NODE>> *sampler_map_;
     const std::unordered_map<VkImageView, VkImageViewCreateInfo> *image_view_map_;
     // TODO : For next 3 maps all we really need (currently) is an image to format mapping
     const std::unordered_map<VkImage, IMAGE_NODE> *image_map_;