Unify the key up/down behaviour of RGB keycodes (#15730)

quantum/process_keycode/process_rgb.c

@@ -51,12 +51,8 @@ static void __attribute__((noinline, unused)) handleKeycodeRGBMode(const uint8_t
  * Handle keycodes for both rgblight and rgbmatrix
  */
 bool process_rgb(const uint16_t keycode, const keyrecord_t *record) {
-#ifndef SPLIT_KEYBOARD
-    if (record->event.pressed) {
-#else
-    // Split keyboards need to trigger on key-up for edge-case issue
+    // need to trigger on key-up for edge-case issue
     if (!record->event.pressed) {
-#endif
 #if (defined(RGBLIGHT_ENABLE) && !defined(RGBLIGHT_DISABLE_KEYCODES)) || (defined(RGB_MATRIX_ENABLE) && !defined(RGB_MATRIX_DISABLE_KEYCODES))
         uint8_t shifted = get_mods() & MOD_MASK_SHIFT;
 #endif