Remove mentions of pip and virtualenv in the install_python_dependencies.sh utility script

[browniebroke]

Description

Following up from:

• Migrate to uv as package manager for the generated project #5434

Checklist:

• I've made sure that tests are updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

We don't need pip or virtualenv anymore.

[foarsitter]

Easy does, Thanks!