Move constant_flow.h into the main library

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index a8c714f..eadf715 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -8,7 +8,7 @@
 #include <test/ssl_helpers.h>
 
 #include <constant_time_internal.h>
-#include <test/constant_flow.h>
+#include "constant_flow.h"
 
 #define SSL_MESSAGE_QUEUE_INIT      { NULL, 0, 0, 0 }