[Content]: Remove the useSubmission/useSubmissions section in the action reference

[amirhhashemi]

📚 Subject area/topic

Reference

📋 Page(s) affected (or suggested, for new content)

https://docs.solidjs.com/solid-router/reference/data-apis/action

📋 Description of content that is out-of-date or incorrect

I think the section on useSubmission/useSubmissions in the action reference page is a bit unnecessary for a few reasons:

1. Both useSubmission and useSubmissions already have their own detailed reference pages.
2. The description there doesn’t really do them justice. They're not just for optimistic updates; they can also handle errors and show pending UI. It’d make more sense to put that info in other guides or reference pages.
3. I checked out the Diataxis Reference Guide (which I assume you use it a reference for writing reference pages), and it says not to mix explanations in reference pages. This section feels more like an explanation to me.

So, I suggest we just remove this section.

Feel free to assign this task to me if you wish.

🖥️ Reproduction in StackBlitz (if reporting incorrect content or code samples)

No response