Remove unused test utility files

These files are dead code - none of them are imported or used anywhere
in the test suite or the collection:
- tests/unit/compat/builtins.py
- tests/unit/mock/loader.py
- tests/unit/mock/path.py
- tests/unit/mock/procenv.py
- tests/unit/mock/vault_helper.py
- tests/unit/mock/yaml_helper.py
- tests/unit/modules/conftest.py
- tests/unit/modules/utils.py

Removing these files also addresses Python 2.7 compatibility concerns
raised in code review, as several contained deprecated imports that
would be incorrect to fix for Python 2.

Also removes corresponding pylint:ansible-bad-import-from entries from
tests/sanity/ignore-2.21.txt.

Related to #686

Co-authored-by: Cursor AI
Signed-off-by: Pavel Bar <pbar@redhat.com>

tests/unit/compat/builtins.py

@@ -1,34 +0,0 @@
-# (c) 2014, Toshio Kuratomi <tkuratomi@ansible.com>
-#
-# This file is part of Ansible
-#
-# Ansible is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# Ansible is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
-
-# Make coding more python3-ish
-from __future__ import (absolute_import, division, print_function)
-__metaclass__ = type
-
-#
-# Compat for python2.7
-#
-
-# One unittest needs to import builtins via __import__() so we need to have
-# the string that represents it
-try:
-    import __builtin__
-except ImportError:
-    BUILTINS = 'builtins'
-else:
-    BUILTINS = '__builtin__'
-    __all__ = ['__builtin__']