Remove QUIC_BUG in when max_datagram_size is 0

It appears to be possible for a WebTransport server to legitimately create a situation where datagrams are enabled but the max datagram size is 0. See the test `ZeroQuicDatagramLimitReturnsZeroMaxDatagramSize` in https://chromium-review.googlesource.com/c/chromium/src/+/8252325/8/net/quic/dedicated_web_transport_http3_client_test.cc

That CL contains a Chromium-side workaround to avoid hitting the `QUIC_BUG()`, but it shouldn't be necessary to work around it in Chromium.

Remove the `QUIC_BUG()` in QUICHE instead.

This code is not used in the GFE.

PiperOrigin-RevId: 969901058

quiche/quic/core/http/quic_spdy_stream.cc

diff --git a/quiche/quic/core/http/quic_spdy_stream.cc b/quiche/quic/core/http/quic_spdy_stream.cc
index 245d6ca..90ae1c2 100644
--- a/quiche/quic/core/http/quic_spdy_stream.cc
+++ b/quiche/quic/core/http/quic_spdy_stream.cc
@@ -1874,10 +1874,6 @@
   QuicByteCount max_datagram_size =
       session()->GetGuaranteedLargestDatagramPayload();
   if (max_datagram_size < prefix_size) {
-    QUIC_BUG(max_datagram_size smaller than prefix_size)
-        << "GetGuaranteedLargestDatagramPayload() returned a datagram size "
-           "that "
-           "is not sufficient to fit stream ID into it.";
     return 0;
   }
   return max_datagram_size - prefix_size;