Remove CLAUDE.md

nf-core core-team consensus is not to allow CLAUDE.md files in pipeline
repos, to avoid this ballooning for other agents and cluttering the
repo root. AGENTS.md remains as the single, tool-agnostic instructions
file; agent-specific loading (e.g. Claude Code treating an AGENTS.md as
if it were a CLAUDE.md) is configured per-user outside the repo instead.

Author: erikrikarddaniel