Remove the obsolete skill notice

[TroyHernandez]

Summary

• Remove the obsolete Posit notice from inst/skills/saber/NOTICE.md, following the maintainer-supplied authorship audit.
• Remove its link and adjacent blank line from inst/skills/saber/SKILL.md.
• Leave all remaining skill instructions, package license metadata, runtime APIs and version unchanged.

Validation

• Base-R comparison confirms the remaining skill text is unchanged and DESCRIPTION matches the base commit exactly.
• Only the two requested files change; staged diff whitespace check passes.
• Source-package build and tarball contents checked separately before handoff.

This is a documentation-only follow-up to #41. No normal package installation or active session is changed.