tokio-quiche: remove debug_assert! in process_write_frame

This debug_assert was introduced in #2166
and can trigger if a stream's FIN frame can't be serialized immediately due to
not having enough congestion window or flow control window.  Sending of the FIN
stream next time window becomes available works correctly, the only problem is
that this debug_assert triggers failures when running download stress tests in debug
mode (in other words, when binaries are build without the --release flag)

Author: antoniovicente

tokio-quiche/src/http3/driver/mod.rs

@@ -703,11 +703,6 @@ impl<H: DriverHooks> H3Driver<H> {
         let Some(frame) = &mut ctx.queued_frame else {
             return Ok(());
         };
-        debug_assert!(
-            ctx.recv.is_some(),
-            "If we have a queued frame in the context, we MUST NOT be waiting
-             on data from the channel"
-        );
 
         let audit_stats = &ctx.audit_stats;
         let stream_id = audit_stats.stream_id();