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/kernel/mempool_persist.cpp

@@ -6,7 +6,6 @@
 
 #include <clientversion.h>
 #include <consensus/amount.h>
-#include <fs.h>
 #include <logging.h>
 #include <primitives/transaction.h>
 #include <serialize.h>
@@ -15,6 +14,7 @@
 #include <sync.h>
 #include <txmempool.h>
 #include <uint256.h>
+#include <util/fs.h>
 #include <util/fs_helpers.h>
 #include <util/time.h>
 #include <validation.h>

src/kernel/mempool_persist.h

@@ -5,7 +5,7 @@
 #ifndef BITCOIN_KERNEL_MEMPOOL_PERSIST_H
 #define BITCOIN_KERNEL_MEMPOOL_PERSIST_H
 
-#include <fs.h>
+#include <util/fs.h>
 
 class Chainstate;
 class CTxMemPool;