Update HTTP 303 redirect behavior in documentation

Removed mention of UserInteractionOptions.UseHttp303Redirects and clarified that IdentityServer now always uses HTTP 303 for redirects from POST endpoints. Updated documentation to reflect compliance with FAPI 2.0.

Author: maartenba

astro/src/content/docs/identityserver/upgrades/v7_4-to-v8_0.md

@@ -238,12 +238,8 @@ dependency. Use the `CancellationToken` passed directly to interface methods ins
 
 ### HTTP 303 Redirects Now Unconditional
 
-`UserInteractionOptions.UseHttp303Redirects` has been removed. IdentityServer now always uses
-HTTP 303 (See Other) for redirects from POST endpoints, in compliance with
-[FAPI 2.0 Section 5.3.2.2](https://openid.net/specs/fapi-2_0-security-profile.html).
-
-No action is needed unless you explicitly set `UseHttp303Redirects = false` in a previous version.
-If so, remove that setting — the redirect behavior can no longer be changed.
+IdentityServer now always uses HTTP 303 (See Other) for redirects from POST endpoints,
+in compliance with [FAPI 2.0 Section 5.3.2.2](https://openid.net/specs/fapi-2_0-security-profile.html).
 
 ### IClientStore.GetAllClientsAsync Now Required