fix(s2n-quic): make AsyncWrite::poll_flush a no-op #4917

Job	Run time
env	4s
s2n-quic-qns (debug)	2m 34s
s2n-quic-qns (release)	7m 13s
h3spec (s2n-tls)	15s
h3spec (rustls)	19s
bench	18m 0s
attack (udp)	5m 27s
interop (aioquic, s2n-quic)	16m 49s
interop (chrome, s2n-quic)	5m 29s
perf (s2n-quic, s2n-quic)	1m 13s
perf (s2n-quic-null, s2n-quic-null)	1m 1s
interop (go-x-net, s2n-quic)	11m 46s
interop (kwik, s2n-quic)	13m 50s
interop (lsquic, s2n-quic)	13m 27s
interop (msquic, s2n-quic)	18m 4s
interop (mvfst, s2n-quic)	11m 30s
interop (neqo, s2n-quic)	15m 33s
interop (ngtcp2, s2n-quic)	14m 0s
interop (picoquic, s2n-quic)	15m 12s
interop (quic-go, s2n-quic)	12m 52s
interop (quiche, s2n-quic)	15m 41s
interop (quinn, s2n-quic)	14m 16s
interop (s2n-quic, aioquic)	13m 13s
interop (s2n-quic, go-x-net)	11m 33s
interop (s2n-quic, haproxy)	11m 16s
interop (s2n-quic, kwik)	13m 5s
interop (s2n-quic, lsquic)	11m 20s
interop (s2n-quic, msquic)	13m 6s
interop (s2n-quic, mvfst)	14m 46s
interop (s2n-quic, neqo)	12m 41s
interop (s2n-quic, nginx)	10m 35s
interop (s2n-quic, ngtcp2)	12m 51s
interop (s2n-quic, picoquic)	11m 56s
interop (s2n-quic, quic-go)	10m 33s
interop (s2n-quic, quiche)	11m 22s
interop (s2n-quic, quinn)	12m 2s
interop (s2n-quic, s2n-quic)	12m 38s
interop (s2n-quic, s2n-quic-rustls)	12m 3s
interop (s2n-quic, xquic)	12m 21s
interop (s2n-quic-rustls, s2n-quic)	12m 31s
interop (xquic, s2n-quic)	18m 26s
perf-report	16s
interop-report	15s
	7h 33m 24s

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