test: functional: drop rmtree usage and add lint check

`shutil.rmtree` is dangerous because it recursively deletes. There are
not likely to be any issues with it's current uses, but it is possible
that some of the assumptions being made now won't always be true, e.g.
about what some of the variables being passed to `rmtree` represent.

For some remaining uses of rmtree that can't be avoided for now, use
`cleanup_dir` which asserts that the recursively deleted folder is a
child of the the `tmpdir` of the test run. Otherwise,
`tempfile.TemporaryDirectory` should be used which does it's own
deleting on being garbage collected, or old fashioned unlinking and
rmdir in the case of directories with known contents.

test/functional/test_framework/test_node.py

@@ -11,7 +11,6 @@ from enum import Enum
 import json
 import logging
 import os
-import pathlib
 import platform
 import re
 import subprocess
@@ -20,7 +19,6 @@ import time
 import urllib.parse
 import collections
 import shlex
-import shutil
 import sys
 from collections.abc import Iterable
 from pathlib import Path
@@ -163,8 +161,8 @@ class TestNode():
                 self.args.append("-ipcbind=unix")
             else:
                 # Work around default CI path exceeding maximum socket path length.
-                self.ipc_tmp_dir = pathlib.Path(tempfile.mkdtemp(prefix="test-ipc-"))
-                self.ipc_socket_path = self.ipc_tmp_dir / "node.sock"
+                self.ipc_tmp_dir = tempfile.TemporaryDirectory(prefix="test-ipc-")
+                self.ipc_socket_path = Path(self.ipc_tmp_dir.name) / "node.sock"
                 self.args.append(f"-ipcbind=unix:{self.ipc_socket_path}")
 
         if self.version_is_at_least(190000):
@@ -248,9 +246,6 @@ class TestNode():
             # this destructor is called.
             print(self._node_msg("Cleaning up leftover process"), file=sys.stderr)
             self.process.kill()
-        if self.ipc_tmp_dir:
-            print(self._node_msg(f"Cleaning up ipc directory {str(self.ipc_tmp_dir)!r}"))
-            shutil.rmtree(self.ipc_tmp_dir)
 
     def __getattr__(self, name):
         """Dispatches any unrecognised messages to the RPC connection or a CLI instance."""