converters/pdf2djvu: Update to 0.9.13

Remove now obsolete patches that were merged by upstream:

• Build fixes for graphics/poppler >= 0.76.0
• Improvement of build-time logging

While I'm here:

• Add path to LICENSE_FILE
• Fix no-op occurence of DOCS_DESC

Changelog:

https://github.com/jwilk/pdf2djvu/blob/0.9.13/doc/changelog

PR: 239366
Submitted by: Samy Mahmoudi <samy.mahmoudi@gmail.com> (maintainer)
MFH: 2019Q4