Revert `Disable Long Polling Fallback Transport for Blazor Server` Breaking Change in RC2

[TanayParikh]

We've reverted enforcing web sockets breaking change for RC2. Consequently, we need to revert the doc changes:

aspnet/Announcements#470

• Update Long Polling content #23333
• Long Polling disabled update #23033

[TanayParikh]

cc/ @guardrex should we just revert the PRs?

[guardrex]

I'll take care of it @TanayParikh. We can't usually revert cleanly because of doc churn. It's easier for me to revert manually in most cases. I'll take care of it tomorrow morning (Wednesday).

[TanayParikh]

Thanks @guardrex!

[guardrex]

I'll mark the PR to hold for RC2 and ping u for review.