Fix comments (#20759)

Marlin/src/feature/mmu/mmu2.cpp

   set_runout_valid(false);
 
   #if PIN_EXISTS(MMU2_RST)
-    // TODO use macros for this
     WRITE(MMU2_RST_PIN, HIGH);
     SET_OUTPUT(MMU2_RST_PIN);
   #endif
 /**
  * Load filament to nozzle of multimaterial printer
  *
- * This function is used only only after T? (user select filament) and M600 (change filament).
+ * This function is used only after T? (user select filament) and M600 (change filament).
  * It is not used after T0 .. T4 command (select filament), in such case, gcode is responsible for loading
  * filament to nozzle.
  */