[nrfconnect] Simplify CMake files (#4524)

* [nrfconnect] Simplify CMake files

Get rid of app.cmake file by leveraging Zephyr standard
mechanisms to:
* automatically link the app with CHIP libraries when
  CHIP is loaded as a Zephyr module.
* automatically pull a Device Tree overlay for a selected
  board into the project.

* Restyled by prettier-markdown

Co-authored-by: Restyled.io <commits@restyled.io>
diff --git a/config/nrfconnect/README.md b/config/nrfconnect/README.md
index 34eafc9..10e2463 100644
--- a/config/nrfconnect/README.md
+++ b/config/nrfconnect/README.md
@@ -3,9 +3,8 @@
 This directory contains build scripts and common configuration files used by
 CHIP nRF Connect applications. It is structured as follows:
 
-| File/Folder   | Contents                                                                                                                                                       |
-| ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| chip-gn       | GN project used to build selected CHIP libraries with the _nrfconnect_ platform integration layer                                                              |
-| chip-module   | CMake wrapper for the GN project defined in `chip-gn` directory, and other components that allow one to use CHIP as a Zephyr module                            |
-| app/app.cmake | Helper CMake module to be used by nRF Connect applications in this repository to inject `chip-module` into the Zephyr module list and load Zephyr build system |
-| app/\*.conf   | Common and optional Kconfig configuration files that can be used in nRF Connect applications                                                                   |
+| File/Folder | Contents                                                                                                                            |
+| ----------- | ----------------------------------------------------------------------------------------------------------------------------------- |
+| chip-gn     | GN project used to build selected CHIP libraries with the _nrfconnect_ platform integration layer                                   |
+| chip-module | CMake wrapper for the GN project defined in `chip-gn` directory, and other components that allow one to use CHIP as a Zephyr module |
+| app         | Common and optional Kconfig configuration files that can be used in nRF Connect applications                                        |