Simplify asciidoctor setup for reference docs

Author: bclozel

spring-graphql-docs/src/docs/asciidoc/attributes.adoc

@@ -1,5 +1,3 @@
-:!version-label:
-:doctype: book
 :idprefix:
 :idseparator: -
 :toc: left
@@ -9,7 +7,6 @@
 :sectanchors:
 :sectnums:
 :hide-uri-scheme:
-:docinfo: shared,private
 :github-tag: main
 :github-repo: spring-projects/spring-graphql
 :github-raw: https://raw.githubusercontent.com/{github-repo}/{github-tag}