chore: Remove use of legacy restore, which is now deprecated

[robbie-duo]

We deprecated the legacy restore feature and, thus, the AdminAPI no longer has the ability to change these values since they no longer exist. This PR removes them from the client!

Description

Removes all use of reactivation_url and reactivation_integration_key from duo_client/admin and updates tests to reflect said changes.

Motivation and Context

• The feature is deprecated and no longer exists!

How Has This Been Tested?

• Tests passed.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Removing deprecated functionality