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

tests/python/deform_modifiers.py

@@ -1,7 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
-# <pep8 compliant>
-
 # To run the test type: blender -b /path/to/the/blend/file --python path/to/this/py/file -- --run-all-tests -- --verbose
 # Type the above line in cmd/terminal, for example, look below
 # blender -b c:\blender-lib\deform_modifiers.blend --python c:\deform_modifiers.py -- --run-all-tests -- --verbose