Revert "Start writing implementation documentation"

This reverts commit 6c59213. This was
supposed to land on a separate branch.

Author: nex3

CONTRIBUTING.md

@@ -9,7 +9,6 @@ Want to contribute? Great! First, read this page.
   * [Synchronizing](#synchronizing)
   * [File Headers](#file-headers)
 * [Release Process](#release-process)
-* [Package Structure](#package-structure)
 
 ## Before You Contribute
 
@@ -234,13 +233,3 @@ few things to do before pushing that tag:
 
 You *don't* need to create tags for packages in `pkg`; that will be handled
 automatically by GitHub actions.
-
-## Package Structure
-
-The structure of the Sass package is documented in README.md files in most
-directories under `lib/`. This documentation is intended to help contributors
-quickly build a basic understanding of the structure of the compiler and how its
-various pieces fit together. [`lib/src/README.md`] is a good starting point to get
-an overview of the compiler as a whole.
-
-[`lib/src/README.md`]: lib/src/README.md