Another comment why all this came up - afais there is *nothing* mentioned in the calibre source code that python2-unrardll is needed, useful, or whatever.
Code:
$ grep -i unrardll `find . -type f`
./src/calibre/utils/unrar.py: from unrardll import extract
./src/calibre/utils/unrar.py: from unrardll import names
./src/calibre/utils/unrar.py: from unrardll import comment
./src/calibre/utils/unrar.py: from unrardll import extract_member
I think it would make sense to document this dependency somewhere ...