CLEANUP: listener: remove the unused handler field

Historically listeners used to have a handler depending on the upper
layer. But now it's exclusively process_stream() and nothing uses it
anymore so it can safely be removed.
diff --git a/include/types/listener.h b/include/types/listener.h
index f309c84..064c040 100644
--- a/include/types/listener.h
+++ b/include/types/listener.h
@@ -190,7 +190,6 @@
 	unsigned int maxaccept;         /* if set, max number of connections accepted at once */
 	struct list proto_list;         /* list in the protocol header */
 	int (*accept)(struct listener *l, int fd, struct sockaddr_storage *addr); /* upper layer's accept() */
-	struct task * (*handler)(struct task *t); /* protocol handler. It is a task */
 	enum obj_type *default_target;  /* default target to use for accepted sessions or NULL */
 	struct list wait_queue;		/* link element to make the listener wait for something (LI_LIMITED)  */
 	unsigned int analysers;		/* bitmap of required protocol analysers */
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 850160f..bdf63c2 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -2075,7 +2075,6 @@
 					l->maxconn = curpeers->peers_fe->maxconn;
 					l->backlog = curpeers->peers_fe->backlog;
 					l->accept = session_accept_fd;
-					l->handler = process_stream;
 					l->analysers |=  curpeers->peers_fe->fe_req_ana;
 					l->default_target = curpeers->peers_fe->default_target;
 					l->options |= LI_O_UNLIMITED; /* don't make the peers subject to global limits */
@@ -9039,7 +9038,6 @@
 			}
 
 			listener->accept = session_accept_fd;
-			listener->handler = process_stream;
 			listener->analysers |= curproxy->fe_req_ana;
 			listener->default_target = curproxy->default_target;
 
diff --git a/src/cli.c b/src/cli.c
index 77db681..47020ff 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -269,7 +269,6 @@
 			l->maxconn = global.stats_fe->maxconn;
 			l->backlog = global.stats_fe->backlog;
 			l->accept = session_accept_fd;
-			l->handler = process_stream;
 			l->default_target = global.stats_fe->default_target;
 			l->options |= LI_O_UNLIMITED; /* don't make the peers subject to global limits */
 			l->nice = -64;  /* we want to boost priority for local stats */