CLEANUP: applet: rename appctx_cs() to appctx_sc()

It returns a stream connector, not a conn_stream anymore, so let's
fix its name.
diff --git a/src/proxy.c b/src/proxy.c
index 02fc3ca..3dc1d24 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -2786,7 +2786,7 @@
 static int cli_io_handler_servers_state(struct appctx *appctx)
 {
 	struct show_srv_ctx *ctx = appctx->svcctx;
-	struct stconn *sc = appctx_cs(appctx);
+	struct stconn *sc = appctx_sc(appctx);
 	struct proxy *curproxy;
 
 	if (ctx->state == SHOW_SRV_HEAD) {
@@ -3138,7 +3138,7 @@
 static int cli_io_handler_show_errors(struct appctx *appctx)
 {
 	struct show_errors_ctx *ctx = appctx->svcctx;
-	struct stconn *sc = appctx_cs(appctx);
+	struct stconn *sc = appctx_sc(appctx);
 	extern const char *monthname[12];
 
 	if (unlikely(sc_ic(sc)->flags & (CF_WRITE_ERROR|CF_SHUTW)))