Remove outdated comment (#18597)

Marlin/Configuration.h

@@ -1162,7 +1162,6 @@
  *
  * RAMPS-based boards use SERVO3_PIN for the first runout sensor.
  * For other boards you may need to define FIL_RUNOUT_PIN, FIL_RUNOUT2_PIN, etc.
- * By default the firmware assumes HIGH=FILAMENT PRESENT.
  */
 //#define FILAMENT_RUNOUT_SENSOR
 #if ENABLED(FILAMENT_RUNOUT_SENSOR)