Remove the non-maintained CMake build system.

It is difficult to maintain one build system, let alone two - especially
if one build system is known to be better maintained and the other build
system continues to be used - with bug and feature requests raised
against it.

The maintainers are aware that there are people using the CMake system,
but believe that the extra maintainability of only having one build
system, combined with the knowledge that the current CI system
demonstrates that all supported architectures are working with the
Makefiles make the use of these Makefiles a more sustainable direction.

doc/Building.md

@@ -47,52 +47,10 @@ these difficulties are being discussed for future n2n versions.
 
 # Build on Windows
 
-The following document some possible windows compile recipes.  Of them, the
-MinGW build process is more tested as it is more friendly to open source
+The following document one possible windows compile recipe.  The reason
+a MinGW build process is used is it is more friendly to open source
 development.
 
-## Visual Studio
-
-### Requirements
-In order to build with Vidual Studio on Windows the following tools should be installed:
-
-- Visual Studio. For a minimal install, the command line only build tools can be
-  downloaded and installed from https://visualstudio.microsoft.com/downloads/#build-tools-for-visual-studio-2017.
-
-- CMake (From https://cmake.org/download/)
-
-  NOTE: You should always use the official cmake stable release as otherwise
-  you may have issues finding libraries (e.g: the installed OpenSSL library).
-  If you still have problems, you can try invoking it with `C:\Program Files\CMake\bin\cmake`.
-
-- (optional) The OpenSSL library.  This optional library can be enabled as
-  per the steps in the [Build time Configuration](BuildConfig.md)
-
-  Pre-built OpenSSL binaries can be downloaded from
-  https://slproweb.com/products/Win32OpenSSL.html.
-  The full version is required, i.e. not the "Light" version. The Win32
-  version of it is usually required for a standard build.
-
-### CLI steps
-
-In order to build from the command line, open a terminal window change to
-the directory where the git checkout of this repository is and run the
-following commands:
-
-Building using `cmake` works as follows:
-
-```batch
-cmake -E make_directory build
-cd build
-
-rem Append any options to the next line
-cmake ..
-
-cmake --build . --config Release
-```
-
-The compiled `.exe` files should now be available in the `build\Release` directory.
-
 ## MinGW
 
 These steps were tested on a fresh install of Windows 10 Pro with all patches