std::deque cleanup in quic_unacked_packet_map.h

quic_unacked_packet_map.h does not use std::deque since cl/356316368.

PiperOrigin-RevId: 372551116
Change-Id: I2e590da21b1b6604fcc05a6f32bae24008cb4c5a
diff --git a/quic/core/quic_unacked_packet_map.h b/quic/core/quic_unacked_packet_map.h
index 67c25f7..676f054 100644
--- a/quic/core/quic_unacked_packet_map.h
+++ b/quic/core/quic_unacked_packet_map.h
@@ -7,7 +7,6 @@
 
 #include <cstddef>
 #include <cstdint>
-#include <deque>
 
 #include "absl/strings/str_cat.h"
 #include "quic/core/quic_packets.h"