Revert "workaround for bogus errors using sed in OS X"
Revert "workaround for bogus errors using sed in OS X"

This reverts commit dedbd6f007550f2f20bc74da60f390337aa5b61c.
Patch does provoke errors for me. I had to revoke it in my branch.
Here the error message under debian 8 with sed (GNU sed) 4.2.2:
can't read s:<(book|article):<!DOCTYPE \1 [<!ENTITYle or directory...

getreu/asciidoctor-fopub,getreu/asciidoctor-fopub,getreu/asciidoctor-fopub