refactor: 미사용 메서드 제거

src/main/java/roomescape/common/dto/response/RoomescapeErrorResponse.kt

@@ -8,11 +8,4 @@ import roomescape.common.exception.ErrorType
 data class RoomescapeErrorResponse(
         val errorType: ErrorType,
         val message: String
-) {
+)
-
-    companion object {
-        @JvmStatic
-        fun of(errorType: ErrorType, message: String? = null): RoomescapeErrorResponse =
-                RoomescapeErrorResponse(errorType, message ?: errorType.description)
-    }
-}