MINOR: quic: Duplicated QUIC_RX_BUFSZ definition

This macro is already defined in src/quic_sock.c which is the correct place.

Must be backported to 2.6
diff --git a/include/haproxy/xprt_quic-t.h b/include/haproxy/xprt_quic-t.h
index 1d530f4..b51779a 100644
--- a/include/haproxy/xprt_quic-t.h
+++ b/include/haproxy/xprt_quic-t.h
@@ -257,8 +257,6 @@
 
 /* Size of the internal buffer of QUIC TX ring buffers (must be a power of 2) */
 #define QUIC_TX_RING_BUFSZ  (1UL << 12)
-/* Size of the internal buffer of QUIC RX buffer. */
-#define QUIC_RX_BUFSZ  (1UL << 18)
 /* Size of the QUIC RX buffer for the connections */
 #define QUIC_CONN_RX_BUFSZ (1UL << 14)