Remove legacy binaries: `http_tracker_client`, `udp_tracker_client`, `tracker_checker`

[josecelano]

Goal

Remove the three legacy client binaries that were deprecated when tracker_client shipped in
issue #1771.

Background

The unified tracker_client binary was introduced in #1771, replacing three separate binaries:

• http_tracker_client → tracker_client http announce|scrape
• udp_tracker_client → tracker_client udp announce|scrape
• tracker_checker → tracker_client check

All three legacy binaries currently:

• Print a deprecation notice on startup directing users to tracker_client.
• Are otherwise frozen — no new features will be added.

Per the deprecation policy in #1771, removal should happen no earlier than approximately one
year after tracker_client is released and documented, to allow external documentation
(Torrust website, blog posts, third-party references) time to be updated.

Scope

• Delete console/tracker-client/src/bin/http_tracker_client.rs
• Delete console/tracker-client/src/bin/udp_tracker_client.rs
• Delete console/tracker-client/src/bin/tracker_checker.rs
• Remove the corresponding [[bin]] entries from console/tracker-client/Cargo.toml
• Delete or fold the legacy module trees:
  • console/tracker-client/src/console/clients/http/ (app.rs only; library code in
    packages/tracker-client is unaffected)
  • console/tracker-client/src/console/clients/udp/ (same caveat)
  • console/tracker-client/src/console/clients/checker/ (or retain if any module code is
    still needed by unified/)
• Update any remaining in-repo references (docs, CI, README).
• Flatten/rename console/tracker-client/src/console/clients/unified/ → top-level
  console/tracker-client/src/console/clients/ if desired (follow-up clean-up, not required).

References

• Parent EPIC: Overhaul clients #669
• Deprecation introduced in: Merge clients into a unified tracker_client CLI (mechanical port) #1771
• Spec: docs/issues/open/1771-merge-clients-into-unified-tracker-client-cli.md (AC9)