Remove the unused "Disable non-blocking IO" QUIC experiment code.

net/http/http_network_session.h

Index: net/http/http_network_session.h
diff --git a/net/http/http_network_session.h b/net/http/http_network_session.h
index a2117e068aefc8ff7b8f5a0823986d63f7510b7f..27725eec450cfc623ba53d6e627b4e2dbe91dcec 100644
--- a/net/http/http_network_session.h
+++ b/net/http/http_network_session.h
@@ -122,8 +122,6 @@ class NET_EXPORT HttpNetworkSession
     // Retry requests which fail with QUIC_PROTOCOL_ERROR, and mark QUIC
     // broken if the retry succeeds.
     bool retry_without_alt_svc_on_quic_errors;
-    // Use non-blocking IO for UDP sockets.
-    bool quic_enable_non_blocking_io;
     // Maximum number of server configs that are to be stored in
     // HttpServerProperties, instead of the disk cache.
     size_t quic_max_server_configs_stored_in_properties;