Correct M401 / M402 description

Marlin/src/gcode/gcode.h

  * M380 - Activate solenoid on active extruder. (Requires EXT_SOLENOID)
  * M381 - Disable all solenoids. (Requires EXT_SOLENOID)
  * M400 - Finish all moves.
- * M401 - Lower Z probe. (Requires a probe)
- * M402 - Raise Z probe. (Requires a probe)
+ * M401 - Deploy and activate Z probe. (Requires a probe)
+ * M402 - Deactivate and stow Z probe. (Requires a probe)
  * M404 - Display or set the Nominal Filament Width: "W<diameter>". (Requires FILAMENT_WIDTH_SENSOR)
  * M405 - Enable Filament Sensor flow control. "M405 D<delay_cm>". (Requires FILAMENT_WIDTH_SENSOR)
  * M406 - Disable Filament Sensor flow control. (Requires FILAMENT_WIDTH_SENSOR)

Marlin/src/gcode/probe/M401_M402.cpp

 #include "../../module/probe.h"
 
 /**
- * M401: Engage Z Servo endstop if available
+ * M401: Deploy and activate the Z probe
  */
 void GcodeSuite::M401() { DEPLOY_PROBE(); }
 
 /**
- * M402: Retract Z Servo endstop if enabled
+ * M402: Deactivate and stow the Z probe
  */
 void GcodeSuite::M402() { STOW_PROBE(); }