Bugfix: Stax shell running issues

Description of change

1. Added ensurepip again because of Linux issue to install pip packages.
2. Removed screencast_keys addon from userpref.blend, added by mistake.

How to test it

Run Stax in CLI.

Checklist

Please check if your MR fulfills the following requirements:

• Unit tests have been added, if needed
• Documentation have been updated, if needed
• Build was run locally and any changes were pushed
• Lint has passed locally without error
• Package.py have been updated, if needed
• CHANGELOG.md have been updated, if needed
• Version numer has been tagged, if needed

FYI: @awesome_dev_too