Revert explainer from instructions file

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jurre

.github/copilot-instructions.md

@@ -1,7 +1,5 @@
 # Dependabot Core AI Agent Instructions
 
-This file contains the core architecture and conventions that apply to all tasks. Additional scoped instructions in `.github/instructions/` are automatically included based on the files you're editing — this keeps each prompt focused and avoids injecting irrelevant context.
-
 ## Architecture Overview
 
 Dependabot Core is a modular Ruby gem collection that updates dependencies across 20+ ecosystems. The architecture follows a plugin pattern where each package manager (e.g., `go_modules`, `bundler`, `npm_and_yarn`) implements the same core interfaces.