tests: check flushing changed its arguments (#1288)

diff --git a/test/nginx_system_test.sh b/test/nginx_system_test.sh
index 3ee6410..1488bad 100644
--- a/test/nginx_system_test.sh
+++ b/test/nginx_system_test.sh
@@ -1366,9 +1366,7 @@
 
 start_test Follow flushes can be turned off.
 echo "Check that FollowFlushes off outputs a single chunk"
-URL="http://noflush.example.com/mod_pagespeed_test/slow_flushing_html_response.php"
-check_flushing "curl -N --raw --silent --proxy $SECONDARY_HOSTNAME $URL" \
-  5.4 1
+check_flushing 5.4 1
 
 start_test Special responses from php are handled OK.
 URL="http://special-response.example.com/A.foo.css.pagespeed.cf.0.css"