Remove the v2 upgrade feature flags

With force-upgrade-v2-encryption on, the clients loop on any v1 account that stays v1 on a vault route: the migration check runs fullSync(false), which writes lastSync, which triggers the scheduler again. No server response stops it, so don't serve the flag until the clients fix it.

pm-30144-sdk-key-rotation and pm-31050-no-logout-key-upgrade-rotation only serve that upgrade, so they go too.

src/api/core/accounts.rs

@@ -1775,8 +1775,7 @@ async fn rotate_account(data: RotateData, headers: Headers, conn: DbConn, nt: No
     // Prevent logging out the client where the user requested this endpoint from.
     // If you do logout the user it will causes issues at the client side.
     // Adding the device uuid will prevent this.
-    // On an upgrade, the reason lets clients sync instead: always from 2026.10.1 (Desktop 2026.10.2), before only
-    // with `pm-31050-no-logout-key-upgrade-rotation`
+    // On an upgrade, the reason lets clients sync instead
     let reason = is_upgrade.then_some(LogOutReason::KeyRotation);
     nt.send_logout_with_reason(&user, Some(&headers.device), reason, &conn).await;