Remove DOGM bottom horizontal line/separator (#18273)

Marlin/src/lcd/dogm/u8g_dev_tft_320x240_upscale_from_128x64.cpp

   void drawImage(const uint8_t *data, u8g_t *u8g, u8g_dev_t *dev, uint16_t length, uint16_t height, uint16_t color) {
     uint16_t buffer[BUTTON_SIZE_X * sq(FSMC_UPSCALE)];
 
-    //NOTE: the buffer are sized for max 32 lenght! If you need draw bigger things with this function, we need increase the buffer
     if (length > BUTTON_SIZE_X) return;
 
     for (uint16_t i = 0; i < height; i++) {
           setWindow = setWindow_ili9328;
           break;
         case 0x9341:   // ILI9341
-        case 0x8066:   // ILI9341 Anycubic / TronXY TFTs      
+        case 0x8066:   // Anycubic / TronXY TFTs (480x320)
           #ifdef LCD_USE_DMA_FSMC
             writeEscSequence(ili9341_init);
           #else
           u8g_WriteSequence(u8g, dev, 160, (uint8_t *)buffer);
       #endif
 
-      // bottom line and buttons
+      // Bottom buttons
       #if ENABLED(TOUCH_BUTTONS)
-
-        setWindow(u8g, dev, BUTTOND_X_LO - 4, BUTTON_Y_LO - 5, BUTTONC_X_HI + BUFSIZE + 4, BUTTON_Y_LO - 4);
-        #ifdef LCD_USE_DMA_FSMC
-          LCD_IO_WriteMultiple(TFT_DISABLED_COLOR, 600 / 2 * FSMC_UPSCALE);
-        #else
-          memset2(buffer, TFT_DISABLED_COLOR, 150);
-          for (uint8_t i = 8; i--;)
-            u8g_WriteSequence(u8g, dev, 150, (uint8_t *)buffer);
-        #endif
-
         setWindow(u8g, dev, BUTTOND_X_LO, BUTTON_Y_LO,  BUTTOND_X_HI, BUTTON_Y_HI);
         drawImage(buttonD, u8g, dev, 32, 20, TFT_BTCANCEL_COLOR);