remove deprecated scan summaries commands

[epalhares-tenchi]

Description

Removes CLI commands that depended on the API endpoints removed.

These commands called the now-deleted SDK methods:

• Client.get_alerts_summaries_scans
• Client.get_following_scan_summaries
• Client.get_alerts_summaries
• Client.get_following_alerts_over_time

Tested

• Ran zanshin --help to ensure removed commands no longer appear.
• Verified all other alerts summary commands execute successfully without errors.
• Test suite passes after cleanup.

Issues Addressed

• References: https://github.com/tenchi-security/zanshin-api/issues/3793