CLEANUP: quid: QUIC draft-28 no more supported

Remove this useless definition.
diff --git a/include/haproxy/xprt_quic-t.h b/include/haproxy/xprt_quic-t.h
index 016703b..4f016df 100644
--- a/include/haproxy/xprt_quic-t.h
+++ b/include/haproxy/xprt_quic-t.h
@@ -45,7 +45,6 @@
 
 typedef unsigned long long ull;
 
-#define QUIC_PROTOCOL_VERSION_DRAFT_28   0xff00001c /* draft-28 */
 #define QUIC_PROTOCOL_VERSION_DRAFT_29   0xff00001d /* draft-29 */
 #define QUIC_PROTOCOL_VERSION_1          0x00000001 /* V1 */
 #define QUIC_PROTOCOL_VERSION_2_DRAFT    0x709a50c4 /* V2 draft */