docs: remove nvidia-device-plugin addon containerd language

[jackfrancis]

Reason for Change:

aks-engine-provided nvidia drivers do work in a containerd configuration, and the addon is installed by default.

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[jackfrancis]

cc @jadarsie @Michael-Sinz

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, Michael-Sinz

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