Cleanup: remove "<pep8 compliant>" from headers

It can be assumed that all scripts comply with basic pep8 formatting
regarding white-space, indentation etc.

Also remove note in best practices page & update `tests/python/pep8.py`.

If we want to exclude some scripts from make format,
this can be done by adding them to `ignore_files` in:
source/tools/utils_maintenance/autopep8_format_paths.py

Or using `# nopep8` for to ignore for individual lines.

Ref T98554

doc/python_api/sphinx_doc_gen_monkeypatch.py

@@ -1,7 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
-# <pep8 compliant>
-
 bpy_types_Operator_bl_property__doc__ = (
     """
 The name of a property to use as this operators primary property.