Fix all issues reported by running: tox -e pep8 and enable pep8 as a linter check

fix(types): prevent __dir__ in RestObject from producing duplicates

The function sanitize_parameters() was used when the v3 API was in
use. Since v3 API support has been removed there are no more users of
this function.

Local variable name is assigned to but never used

https://www.flake8rules.com/rules/F841.html

F401: Module imported but unused

https://www.flake8rules.com/rules/F401.html

E711: Comparison to none should be 'if cond is none:'

https://www.flake8rules.com/rules/E711.html

E712: Comparison to true should be 'if cond is true:' or 'if cond:'

https://www.flake8rules.com/rules/E712.html

Fixes to resolve errors for:
    https://www.flake8rules.com/rules/E741.html
      Do not use variables named 'I', 'O', or 'l' (E741)

    https://www.flake8rules.com/rules/E742.html
      Do not define classes named 'I', 'O', or 'l' (E742)