MINOR: connection: do not check for CO_FL_SOCK_RD_SH too early

The handshake functions dedicated to proxy proto, netscaler and
socks4 all check for this flag before proceeding. This is wrong,
they must not do and instead perform the call to recv() then
report the close. The reason for this is that the current
construct managed to lose the CO_ER_CIP_EMPTY error code in case
the connection was already shut, thus causing a race condition
with some errors being reported correctly or as unknown depending
on the timing.
diff --git a/src/connection.c b/src/connection.c
index dcecf14..83790a9 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -493,10 +493,6 @@
 	int tlv_offset = 0;
 	int ret;
 
-	/* we might have been called just after an asynchronous shutr */
-	if (conn->flags & CO_FL_SOCK_RD_SH)
-		goto fail;
-
 	if (!conn_ctrl_ready(conn))
 		goto fail;
 
@@ -825,10 +821,6 @@
 	uint8_t ip_ver;
 	int ret;
 
-	/* we might have been called just after an asynchronous shutr */
-	if (conn->flags & CO_FL_SOCK_RD_SH)
-		goto fail;
-
 	if (!conn_ctrl_ready(conn))
 		goto fail;
 
@@ -1094,10 +1086,6 @@
 	char line[SOCKS4_HS_RSP_LEN];
 	int ret;
 
-	/* we might have been called just after an asynchronous shutr */
-	if (conn->flags & CO_FL_SOCK_RD_SH)
-		goto fail;
-
 	if (!conn_ctrl_ready(conn))
 		goto fail;