[#54] fix: ValidationErrorMessage 코드 중복 수정

Author: pythonstrup

src/main/java/com/nexters/teamace/common/exception/ValidationErrorMessage.java

@@ -11,8 +11,6 @@ public class ValidationErrorMessage {
     public static final String USER_ID_POSITIVE = "User ID must be greater than or equal to 1";
     public static final String USERNAME_SIZE = "Username must be between 1 and 20 characters";
 
-    public static final String USER_ID_NOT_NULL = "User ID cannot be null";
-    public static final String USER_ID_POSITIVE = "User ID must be greater than or equal to 1";
     public static final String NICKNAME_SIZE = "Nickname must be between 1 and 20 characters";
     public static final String USERNAME_NOT_BLANK = "username must not be blank";
     public static final String NICKNAME_NOT_BLANK = "nickname must not be blank";