"Download: Built-in" seems to be contradictory to "It was removed in MediaWiki 1.22". Where can users find the "MySkin" skin now?
Topic on Skin talk:MySkin
You can clone the monobook skin and name it MySkin or something else (i.e. None) and remove all the css but the ones that can only be shown in reading mode to prevent the Navigation Menu heading appear. I have made it in my test private localhost server with MW 1.25.2 and did it by myself.