virtualenvwrapper plugin fix #112852 - #12853

when we're not in enabled mode and DISABLE_VENV_CD=1:

• safely delete the chpwd hook workon_cwd if it were previously set up

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

• see the diff :)

Other comments:

• tested only manually

...