refactor: Extract delete logic endpoint

[tshuli]

Problem

Closes #1490

Tests

• Create a form with single logic.
  • Check that delete logic works on admin view Logic Tab. The network call should return 200.
  • Repeat the above with multiple logic. Check that only one logic is deleted.
• Test using manual API calls
  • Check that new delete endpoint DELETE /forms/:formId/logic/:logicId returns 200 when formId and logicId are correct and that the specific logicId is deleted from db
  • Check that endpoint returns 404 when formId or logicId are incorrect

[karrui]

some changes~

[tshuli]

@karrui thanks for reviewing, for re-review please

[tshuli]

@karrui thanks for reviewing, for re-review pls

[karrui]

some more changes;

will the changes to make client use this endpoint will be in a separate PR or was it just missed?

[tshuli]

@karrui simplified the return; frontend changes will come in separate PR

[tshuli]

@karrui actually I added on the frontend changes, for review pls

[karrui]

some changes on the frontend handling requested, lgtm otherwise

[tshuli]

@mantariksh thanks for reviewing, for re-review pls

[tshuli]

@mantariksh thanks for reviewing, for re-review pls