remove workaround for broken footnote xref in Asciidoctor 2.0.11
remove workaround for broken footnote xref in Asciidoctor 2.0.11

Hextremist/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,Hextremist/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,dsisnero/asciidoctor-pdf,dsisnero/asciidoctor-pdf