Drop extraneous calls to lcd_update

Marlin/Marlin_main.cpp

@@ -6463,7 +6463,6 @@ inline void gcode_M140() {
     #if ENABLED(ULTIPANEL)
       powersupply = true;
       LCD_MESSAGEPGM(WELCOME_MSG);
-      lcd_update();
     #endif
   }
 
@@ -6496,7 +6495,6 @@ inline void gcode_M81() {
       powersupply = false;
     #endif
     LCD_MESSAGEPGM(MACHINE_NAME " " MSG_OFF ".");
-    lcd_update();
   #endif
 }