converters/bibtexconv: Update 2.1.0 => 2.1.1

Changelog:
https://github.com/dreibh/bibtexconv/blob/bibtexconv-2.1.1/ChangeLog

Commit log:
https://github.com/dreibh/bibtexconv/compare/bibtexconv-2.1.0...bibtexconv-2.1.1

While here remove python version from USES.

PR: 293441 291526