Remove anchor workaround for GitHub

Author: mojavelinux

demo.adoc

@@ -27,12 +27,6 @@ endif::[]
 This is a demonstration of {library} {asciidoctor-version}.
 And this is the preamble of this document.
 
-ifdef::env-github[]
-++++
-<a name="purpose"></a>
-++++
-endif::env-github[]
-
 [[purpose]]
 .Purpose
 ****