[hotfix] 창작문제 컨펌 가능하도록 수정

Author: seokbeom00

src/main/java/com/moplus/moplus_server/domain/problem/domain/problem/Problem.java

@@ -164,7 +164,6 @@ public void deleteChildProblem(Long childProblemId) {
 
     public boolean isValid() {
         return problemCustomId != null
-                && practiceTestId != null
                 && problemType != null
                 && title != null && !title.getTitle().isEmpty()
                 && answer != null && !answer.getValue().isEmpty()