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/qt/walletframe.cpp

@@ -4,7 +4,6 @@
 
 #include <qt/walletframe.h>
 
-#include <fs.h>
 #include <node/interface_ui.h>
 #include <psbt.h>
 #include <qt/guiutil.h>
@@ -12,6 +11,7 @@
 #include <qt/psbtoperationsdialog.h>
 #include <qt/walletmodel.h>
 #include <qt/walletview.h>
+#include <util/fs.h>
 #include <util/fs_helpers.h>
 
 #include <cassert>