LEDControl: Remove the deprecated LEDControl::mode_add() method

This has been deprecated in March, 2019, has been a no-op since. While no
removal schedule was posted at the time, I believe it is safe to drop it now.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

docs/UPGRADING.md

@@ -570,6 +570,10 @@ The following headers and names have changed:
 
 After the introduction of the new device API, the old APIs (`ROWS`, `COLS`, `LED_COUNT`, `KeyboardHardware`, the old `Hardware` base class, etc) were removed on **2020-06-16**.
 
+#### `LEDControl.mode_add()`
+
+Since March of 2019, this method has been deprecated, and turned into a no-op. While no removal date was posted at the time, after more than a year of deprecation, it has been removed on **2020-06-16**.
+
 ### Removed on 2020-01-06
 
 #### EEPROMKeymap mode

src/kaleidoscope/plugin/LEDControl.h

@@ -25,11 +25,6 @@
 #define Key_LEDEffectPrevious Key(1, KEY_FLAGS | SYNTHETIC | IS_INTERNAL | LED_TOGGLE)
 #define Key_LEDToggle Key(2, KEY_FLAGS | SYNTHETIC | IS_INTERNAL | LED_TOGGLE)
 
-#define _DEPRECATED_MESSAGE_LED_CONTROL_MODE_ADD                               \
-  "LEDControl::mode_add(LEDMode *mode) is deprecated. LEDModes are now \n"     \
-  "automatically registered. You can safely remove any calls to \n"            \
-  "LEDControl::mode_add from your code."
-
 namespace kaleidoscope {
 namespace plugin {
 
@@ -82,11 +77,6 @@ class LEDControl : public kaleidoscope::Plugin {
     cur_led_mode_->onActivate();
   }
 
-  DEPRECATED(LED_CONTROL_MODE_ADD)
-  static int8_t mode_add(LEDMode *mode) {
-    return 0;
-  }
-
   static void setCrgbAt(uint8_t led_index, cRGB crgb);
   static void setCrgbAt(KeyAddr key_addr, cRGB color);
   DEPRECATED(ROW_COL_FUNC) static void setCrgbAt(byte row, byte col, cRGB color) {