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-

ci/test/06_script_b.sh

@@ -44,7 +44,7 @@ if [ "${RUN_TIDY}" = "true" ]; then
           " src/dbwrapper.cpp"\
           " src/init"\
           " src/kernel"\
-          " src/mempool_args.cpp"\
+          " src/node/mempool_args.cpp"\
           " src/node/chainstate.cpp"\
           " src/policy/feerate.cpp"\
           " src/policy/packages.cpp"\