refactor(be): 사용하지 않는 서비스로직 삭제

Author: beekeeper24

src/main/kotlin/com/back/koreaTravelGuide/domain/userChat/chatmessage/service/ChatMessageService.kt

@@ -25,11 +25,6 @@ class ChatMessageService(
         afterId: Long,
     ): List<ChatMessage> = messageRepository.findByRoomIdAndIdGreaterThanOrderByIdAsc(roomId, afterId)
 
-    @Transactional
-    fun deleteByRoom(roomId: Long) {
-        messageRepository.deleteByRoomId(roomId)
-    }
-
     @Transactional
     fun send(
         roomId: Long,