Simplify code style and avoid explaining check modules

Author: petk

docs/cmake/cmake-code-style.md

@@ -9,7 +9,6 @@ ecosystem.
 * [2. General guidelines](#2-general-guidelines)
   * [2.1. End commands](#21-end-commands)
   * [2.2. Source and binary directories](#22-source-and-binary-directories)
-  * [2.3. Check modules](#23-check-modules)
 * [3. Variables](#3-variables)
   * [3.1. Variable scope](#31-variable-scope)
     * [3.1.1. Local variables](#311-local-variables)
@@ -193,21 +192,6 @@ these variables become distinct.
   project source and build directories from the most recent
   `project(ProjectName ...)` call.
 
-### 2.3. Check modules
-
-* Use `check_compiler_flag()`, `check_source_compiles()`, `check_source_runs()`
-  instead of language-specific `check_<LANG>_...()`.
-
-* For checking header files, use `CheckIncludeFiles` module instead of
-  `CheckIncludeFile` or `CheckIncludeFileCXX`. It simplifies and unifies
-  checking single or multiple headers into a common usage across the code.
-
-  ```cmake
-  include(CheckIncludeFiles)
-  check_include_files(sys/types.h HAVE_SYS_TYPES_H)
-  check_include_files("sys/socket.h;net/if.h" HAVE_NET_IF_H)
-  ```
-
 ## 3. Variables
 
 ### 3.1. Variable scope