refactor: Move fs.* to util/fs.*

The fs.* files are already part of the libbitcoin_util library. With the
introduction of the fs_helpers.* it makes sense to move fs.* into the
util/ directory as well.

src/test/script_tests.cpp

@@ -6,7 +6,6 @@
 #include <test/data/bip341_wallet_vectors.json.h>
 
 #include <core_io.h>
-#include <fs.h>
 #include <key.h>
 #include <rpc/util.h>
 #include <script/script.h>
@@ -19,6 +18,7 @@
 #include <test/util/random.h>
 #include <test/util/setup_common.h>
 #include <test/util/transaction_utils.h>
+#include <util/fs.h>
 #include <util/strencodings.h>
 #include <util/system.h>