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/ssl_ckch.c b/src/ssl_ckch.c
index 3ac7ae5..f574fc4 100644
--- a/src/ssl_ckch.c
+++ b/src/ssl_ckch.c
@@ -2044,7 +2044,7 @@
 static int cli_io_handler_commit_cert(struct appctx *appctx)
 {
 	struct commit_cert_ctx *ctx = appctx->svcctx;
-	struct stconn *sc = appctx_cs(appctx);
+	struct stconn *sc = appctx_sc(appctx);
 	int y = 0;
 	char *err = NULL;
 	struct ckch_store *old_ckchs, *new_ckchs = NULL;
@@ -2785,7 +2785,7 @@
 static int cli_io_handler_commit_cafile_crlfile(struct appctx *appctx)
 {
 	struct commit_cacrlfile_ctx *ctx = appctx->svcctx;
-	struct stconn *sc = appctx_cs(appctx);
+	struct stconn *sc = appctx_sc(appctx);
 	int y = 0;
 	char *err = NULL;
 	struct cafile_entry *old_cafile_entry = NULL, *new_cafile_entry = NULL;