fix(fs-delete/webhook): use fs instance instead of historical

[gagantrivedi]

Thanks for submitting a PR! Please check the boxes below:

• I have run pre-commit to check linting
• I have added information to docs/ if required so people know about the feature!
• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

Use feature state instance for delete feature webhook instead of historical instance (because historical record does not exist for feature states created before we introduced history and for some reason they also did not exists for the feature here: https://flagsmith.sentry.io/issues/4929553990/?project=5544478&query=is%3Aunresolved&referrer=issue-stream&statsPeriod=24h&stream_index=19)

How did you test this code?

Add new unit test

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: api/features/tasks.py

Function	Unhandled Issue
trigger_feature_state_change_webhooks	AttributeError: 'NoneType' object has no attribute 'instance' /api/v1/projects/{project_pk}/f... Event Count: 8

---

_{Did you find this useful? React with a 👍 or 👎}

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	Feb 28, 2024 7:19am
flagsmith-frontend-preview	✅ Ready (Inspect)	Visit Preview	Feb 28, 2024 7:19am
flagsmith-frontend-staging	✅ Ready (Inspect)	Visit Preview	Feb 28, 2024 7:19am

[github-actions]

Uffizzi Preview deployment-47402 was deleted.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.91%. Comparing base (76def7c) to head (8c19bca).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3475   +/-   ##
=======================================
  Coverage   95.91%   95.91%           
=======================================
  Files        1092     1092           
  Lines       33991    34006   +15     
=======================================
+ Hits        32601    32616   +15     
  Misses       1390     1390           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.