Update M17_M18_M84.cpp

Marlin/src/gcode/control/M17_M18_M84.cpp

     stepper_inactive_time = parser.value_millis_from_seconds();
   }
   else {
-    bool all_axis = !((parser.seen('X')) || (parser.seen('Y')) || (parser.seen('Z')) || (parser.seen('E')));
+    bool all_axis = !(parser.seen('X') || parser.seen('Y') || parser.seen('Z') || parser.seen('E'));
     if (all_axis) {
       stepper.finish_and_disable();
     }