docs: Make labels consistent; remove boilerplate

- Update labels so they use consistent naming. Instead of the
  copy-and-pasted `chapter` prefix, name labels with a prefix consistent
  with what they point to:
  - "module-" for module
  - "target-" for targets
  - "docs-" for general documentation
- Remove the unnecessary highlight and default-domain directives.
  Neither is necessary since the Pigweed docs always specify the
  language in code snippets and other directives.

Change-Id: I55c34e9ec919f6f4670e5d3d008e0edf5fecf05b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/19328
Commit-Queue: Wyatt Hepler <hepler@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
diff --git a/docs/module_structure.rst b/docs/module_structure.rst
index f3556b3..89ec692 100644
--- a/docs/module_structure.rst
+++ b/docs/module_structure.rst
@@ -1,8 +1,4 @@
-.. default-domain:: cpp
-
-.. highlight:: sh
-
-.. _chapter-module-guide:
+.. _docs-module-structure:
 
 ----------------
 Module Structure
@@ -264,8 +260,8 @@
 
     - Add in ``docs/BUILD.gn`` to ``pw_doc_gen("docs")``
 
-11. Run :ref:`chapter-module-module-check`
+11. Run :ref:`module-pw_module-module-check`
 
     - ``$ pw module-check {pw_module_dir}``
 
-12. Contribute your module to upstream Pigweed (optional but encouraged!)
\ No newline at end of file
+12. Contribute your module to upstream Pigweed (optional but encouraged!)