tests: Reduce compilation time and unneccessary recompiles by removing unused includes in tests

src/test/flatfile_tests.cpp

@@ -2,8 +2,11 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <clientversion.h>
 #include <flatfile.h>
+#include <streams.h>
 #include <test/setup_common.h>
+#include <util/system.h>
 
 #include <boost/test/unit_test.hpp>