chore(docs): remove SFS references and related files

[wolfcito]

What was done:

• Removed all SFS-related markdown files, including guides for registration, withdrawal, and checks.
• Deleted associated assets (e.g., images used for SFS guides).
• Updated SUMMARY.md and other references to ensure no traces of SFS remain.
• Adjusted related sections to maintain documentation coherence without SFS.

Why:

The SFS contract was part of the first season of Mode Network but has been deprecated. Continuing to include outdated references could lead to confusion among developers and users. This PR ensures the documentation is up-to-date and aligned with the current state of the network.

Impact:

• No impact on existing functionality, as this is strictly a documentation update.
• Improved clarity and relevance of the documentation for Mode Network.