CLEANUP: connection: remove unused field idle_time from the connection struct

Thanks to previous changes, this field is now unused.
diff --git a/include/haproxy/connection-t.h b/include/haproxy/connection-t.h
index c00b94e..efeb714 100644
--- a/include/haproxy/connection-t.h
+++ b/include/haproxy/connection-t.h
@@ -489,7 +489,6 @@
 	struct sockaddr_storage *src; /* source address (pool), when known, otherwise NULL */
 	struct sockaddr_storage *dst; /* destination address (pool), when known, otherwise NULL */
 	char *proxy_authority;	      /* Value of authority TLV received via PROXYv2 */
-	unsigned int idle_time;                 /* Time the connection was added to the idle list, or 0 if not in the idle list */
 	uint8_t proxy_authority_len;  /* Length of authority TLV received via PROXYv2 */
 	struct ist proxy_unique_id;  /* Value of the unique ID TLV received via PROXYv2 */
 };
diff --git a/include/haproxy/connection.h b/include/haproxy/connection.h
index a1740b9..05e85e1 100644
--- a/include/haproxy/connection.h
+++ b/include/haproxy/connection.h
@@ -328,7 +328,6 @@
 	MT_LIST_INIT(&conn->list);
 	LIST_INIT(&conn->session_list);
 	conn->subs = NULL;
-	conn->idle_time = 0;
 	conn->src = NULL;
 	conn->dst = NULL;
 	conn->proxy_authority = NULL;
diff --git a/include/haproxy/server.h b/include/haproxy/server.h
index 5ed5837..0686ab1 100644
--- a/include/haproxy/server.h
+++ b/include/haproxy/server.h
@@ -242,7 +242,6 @@
 static inline void srv_use_idle_conn(struct server *srv, struct connection *conn)
 {
 	if (conn->flags & CO_FL_LIST_MASK) {
-		conn->idle_time = 0;
 		_HA_ATOMIC_SUB(&srv->curr_idle_conns, 1);
 		_HA_ATOMIC_SUB(conn->flags & CO_FL_SAFE_LIST ? &srv->curr_safe_nb : &srv->curr_idle_nb, 1);
 		_HA_ATOMIC_SUB(&srv->curr_idle_thr[tid], 1);
@@ -315,7 +314,6 @@
 		}
 		_HA_ATOMIC_SUB(&srv->curr_used_conns, 1);
 		MT_LIST_DEL(&conn->list);
-		conn->idle_time = now_ms;
 		if (is_safe) {
 			conn->flags = (conn->flags & ~CO_FL_LIST_MASK) | CO_FL_SAFE_LIST;
 			MT_LIST_ADDQ(&srv->safe_conns[tid], (struct mt_list *)&conn->list);