Remove the generation by direct calling of asciidoctor

In order to ensure repeatable book builds and cut down any issues
concerning rendering, the build is only ensured through the
installation of the required versions with bundle and the run of the
Rakefile.

This closes #1039

Author: jnavila

README.asc

@@ -30,20 +30,6 @@ Converting to PDF...
  -- PDF output at progit.pdf
 ----
 
-An alternative to calling the `bundle` command is to call directly the `asciidoctor` command.
-
-Use the following commands:
-
-----
-$ asciidoctor progit.asc
-$ asciidoctor-pdf progit.asc
-$ asciidoctor-epub3 progit.asc
-$ asciidoctor-epub3 -a ebook-format=kf8 progit.asc
-----
-
-Both use the `asciidoctor`, `asciidoctor-pdf` and `asciidoctor-epub` projects.
-
-
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