chore(tasks) Remove docs for celery tasks (#15776)

## DESCRIBE YOUR PR

- Remove docs for celery tasks. It has been a few months since we
removed this subsystem and I don't think we need the docs anymore.
- Add a redirect so that bookmarks/links end up in roughly the right
place.

## IS YOUR CHANGE URGENT?  

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to go live.
- [ ] Urgent deadline (GA date, etc.): <!-- ENTER DATE HERE -->
- [ ] Other deadline: <!-- ENTER DATE HERE -->
- [x] None: Not urgent, can wait up to 1 week+

## SLA

- Teamwork makes the dream work, so please add a reviewer to your PRs.
- Please give the docs team up to 1 week to review your PR unless you've
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Thanks in advance for your help!

## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [ ] Checked Vercel preview for correctness, including links
- [ ] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
- [ ] PR was reviewed and approved by a member of the [Sentry docs
team](https://github.com/orgs/getsentry/teams/docs)

Author: markstory

develop-docs/backend/application-domains/asynchronous-workers.mdx

@@ -231,7 +231,7 @@ def do_work() -> None:
     ...
 ```
 
-New activations will be created using `name`. However, both task names will be registered and can process activations. Workers will handle tasks sent to either `do_work_v2` or `do_work` with the same function. 
+New activations will be created using `name`. However, both task names will be registered and can process activations. Workers will handle tasks sent to either `do_work_v2` or `do_work` with the same function.
 
 ### Moving to a Different Namespace
 

develop-docs/backend/application-domains/tasks/index.mdx

@@ -218,6 +218,10 @@ const developerDocsRedirects = [
     source: '/services/emails/',
     destination: '/backend/emails/',
   },
+  {
+    source: '/backend/application-domains/asynchronous-workers/',
+    destination: '/backend/application-domains/tasks/',
+  },
   {
     source: '/self-hosted/custom-ca-roots/',
     destination: '/self-hosted/configuration/custom-ca-roots/',