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/node/blockstorage.cpp

@@ -8,7 +8,6 @@
 #include <clientversion.h>
 #include <consensus/validation.h>
 #include <flatfile.h>
-#include <fs.h>
 #include <hash.h>
 #include <logging.h>
 #include <kernel/chainparams.h>
@@ -18,6 +17,7 @@
 #include <signet.h>
 #include <streams.h>
 #include <undo.h>
+#include <util/fs.h>
 #include <util/syscall_sandbox.h>
 #include <util/system.h>
 #include <validation.h>