Flag unused variables without buzzer (#15016)

Marlin/src/lcd/menu/menu.cpp

     #if HAS_BUZZER
       ui.completion_feedback(saved);
     #endif
+    UNUSED(saved);
   }
   void lcd_load_settings() {
     const bool loaded = settings.load();
     #if HAS_BUZZER
       ui.completion_feedback(loaded);
     #endif
+    UNUSED(loaded);
   }
 #endif
 

Marlin/src/lcd/menu/menu_advanced.cpp

           #if HAS_BUZZER
             ui.completion_feedback(inited);
           #endif
+          UNUSED(inited);
         },
         ui.goto_previous_screen,
         PSTR(MSG_INIT_EEPROM), nullptr, PSTR("?")

platformio.ini

 build_unflags = -std=gnu++11 -DCONFIG_MAPLE_MINI_NO_DISABLE_DEBUG=1
 src_filter    = ${common.default_src_filter} +<src/HAL/HAL_STM32F1>
 lib_deps      = ${common.lib_deps}
-lib_ignore    = Adafruit NeoPixel, SPI
+lib_ignore    = Adafruit NeoPixel, LiquidTWI2, SPI
 
 #
 # MKS Robin (STM32F103ZET6)