Move random test util code from setup_common to random

as many of the unit tests don't use this code

src/test/pmt_tests.cpp

@@ -6,6 +6,7 @@
 #include <merkleblock.h>
 #include <serialize.h>
 #include <streams.h>
+#include <test/util/random.h>
 #include <test/util/setup_common.h>
 #include <uint256.h>
 #include <version.h>