scripted-diff: Move mempool_args to src/node

It is part of the node library. Also, it won't be moved to the kernel
lib, as it will be pruned of ArgsManager.

-BEGIN VERIFY SCRIPT-
 # Move module
 git mv src/mempool_args.cpp src/node/
 git mv src/mempool_args.h   src/node/
 # Replacements
 sed -i 's:mempool_args\.h:node/mempool_args.h:g'     $(git grep -l mempool_args)
 sed -i 's:mempool_args\.cpp:node/mempool_args.cpp:g' $(git grep -l mempool_args)
 sed -i 's:MEMPOOL_ARGS_H:NODE_MEMPOOL_ARGS_H:g'      $(git grep -l MEMPOOL_ARGS_H)
-END VERIFY SCRIPT-

src/test/fuzz/validation_load_mempool.cpp

@@ -5,7 +5,7 @@
 #include <kernel/mempool_persist.h>
 
 #include <chainparamsbase.h>
-#include <mempool_args.h>
+#include <node/mempool_args.h>
 #include <node/mempool_persist_args.h>
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>