style: 불필요한 주석 삭제

Author: Ji-minhyeok

src/main/java/com/threestar/trainus/domain/lesson/student/service/StudentLessonService.java

@@ -221,7 +221,7 @@ public LessonApplicationResponseDto applyToLessonWithLock(Long lessonId, Long us
 				.user(user)
 				.build();
 			lessonParticipantRepository.save(participant);
-			lesson.incrementParticipantCount(); // 비관적 락 덕분에 안전하게 증가
+			lesson.incrementParticipantCount();
 
 			return LessonApplyMapper.toLessonApplicationResponseDto(
 				lesson.getId(),