[chore](planner) remove useless NullableTuples in PlanNode

[morrySnow]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • [ ] Regression test
  • [ ] Unit Test
  • [ ] Manual test (add detailed scripts or steps below)
  • [x] No need to test or manual test. Explain why:
    • [ ] This is a refactor/code format and no logic has been changed.
    • [x] Previous test can cover this change.
    • [ ] No code files have been changed.
    • [ ] Other reason

• Behavior changed:

  • [x] No.
  • [ ] Yes.

• Does this need documentation?

  • [x] No.
  • [ ] Yes.

Check List (For Reviewer who merge this PR)

• [ ] Confirm the release note
• [ ] Confirm test cases
• [ ] Confirm document
• [ ] Add branch pick label