add missing SLIM_LCD_MENUS checks

[ellensp]

Description

Since #27393 SLIM_LCD_MENUS is broken.

When SLIM_LCD_MENUS is enabled void _lcd_toggle_bed_leveling() is not defined.
resulting in this error

In file included from Marlin/src/lcd/menu/menu_probe_level.cpp:31:0:
Marlin/src/lcd/menu/menu_probe_level.cpp: In function 'void menu_probe_level()':
Marlin/src/lcd/menu/menu_probe_level.cpp:274:56: error: '_lcd_toggle_bed_leveling' was not declared in this scope
         EDIT_ITEM(bool, MSG_BED_LEVELING, &show_state, _lcd_toggle_bed_leveling);
                                                        ^
Marlin/src/lcd/menu/menu_item.h:290:39: note: in definition of macro '_MENU_INNER_F'

Added missing SLIM_LCD_MENUS checks.

Requirements

#define SLIM_LCD_MENUS
A probe I used #define FIX_MOUNTED_PROBE
A LCD I used REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER
Bed leveling I used AUTO_BED_LEVELING_UBL
and to satify the requirments
#define Z_SAFE_HOMING
#define EEPROM_SETTINGS

Benefits

Builds as expected

Configurations

Configuration.zip