Remove deprecated Layer API functions as per the schedule

docs/UPGRADING.md

@@ -338,7 +338,7 @@ The layer system used to be index-ordered, meaning that we'd look keys up on
 layers based on the _index_ of active layers. Kaleidoscope now uses activation
 order, which looks up keys based on the order of layer activation.
 
-This means that the following functions are deprecated, and will be removed by **2020-12-31**:
+The following functions have been removed as of **2021-01-01**:
 
 - `Layer.top()`, which used to return the topmost layer index. Use
   `Layer.mostRecent()` instead, which returns the most recently activated layer.

src/kaleidoscope/layers.h

@@ -96,24 +96,14 @@ class Layer_ {
   static void activate(uint8_t layer);
   static void deactivate(uint8_t layer);
   static void activateNext();
-  static void deactivateTop() DEPRECATED(LAYER_DEACTIVATETOP) {
-    deactivateMostRecent();
-  }
   static void deactivateMostRecent();
   static void move(uint8_t layer);
 
-  static uint8_t top(void) DEPRECATED(LAYER_TOP) {
-    return mostRecent();
-  }
   static uint8_t mostRecent() {
     return active_layers_[active_layer_count_ - 1];
   }
   static boolean isActive(uint8_t layer);
 
-  static uint32_t getLayerState(void) DEPRECATED(LAYER_GETLAYERSTATE) {
-    return layer_state_;
-  }
-
   static Key eventHandler(Key mappedKey, KeyAddr key_addr, uint8_t keyState);
 
   typedef Key(*GetKeyFunction)(uint8_t layer, KeyAddr key_addr);

src/kaleidoscope_internal/deprecations.h

@@ -33,16 +33,3 @@
   "For further information and examples on how to do that, \n"           __NL__ \
   "please see UPGRADING.md"
 
-#define _DEPRECATED_MESSAGE_LAYER_DEACTIVATETOP  __NL__ \
-  "`Layer.deactivateTop()` is deprecated.\n"     __NL__ \
-  "Please use `Layer.deactivateMostRecent()` instead."
-
-#define _DEPRECATED_MESSAGE_LAYER_TOP __NL__ \
-  "`Layer.top()` is deprecated.\n"    __NL__ \
-  "Please use `Layer.mostRecent()` instead."
-
-#define _DEPRECATED_MESSAGE_LAYER_GETLAYERSTATE    __NL__ \
-  "`Layer.getLayerState()` is deprecated.\n"       __NL__ \
-  "Layers are now in activation-order, please use" __NL__ \
-  "`Layer.forEachActiveLayer()` instead."
-