Remove ansible-core 2.20 deprecated imports

[rjeffman]

This patch removes all dependencies on the 'asible.module_util.six'
module and fixes deprecated imports as defined by the ansible-core
release version 2.20.

This changes render ansible-freeipa collection incompatible with
Python 2.

Changes include:

• Remove six module imports from all modules and roles

  • Removed 'from ansible.module_utils import six' statements
  • Removed 'from ansible.module_utils.six.moves' imports

• Replace and remove Python version checks (six.PY3 and six.PY2)

• Replace unicode usage with to_text or str

• Ensure text conversion routines imports are consistent and are
  imported from Ansible common.text.converters

• Update standard library imports

  • Changed 'six.moves.urllib.parse' to 'urllib.parse'
  • Changed 'six.moves.configparser' to 'ConfigParser'
  • Import 'Mapping' from 'collections.abc'

• Remove Python 2 specific code

Note that this change only addresses the deprecation issues
with ansible-core 2.20. For full migration from Python 2 the
minimum supported IPA version should be 4.9, that currently targets
Python 3.6.

Fixes #1399

Summary by Sourcery

Remove deprecated ansible.module_utils.six usage and Python 2 compatibility code to comply with ansible-core 2.20 deprecations.

Enhancements:

• Remove all imports and usage of ansible.module_utils.six and eliminate Python 2 specific branches.
• Replace unicode references with str or to_text and consolidate text conversion imports from ansible.module_utils.common.text.converters.
• Update standard library imports to modern modules (urllib.parse, ConfigParser, collections.abc.Mapping).
• Revise certificate tests to use regex matching for "not found" messages instead of hardcoded substrings.