Revert "adds "wordlists/wordlist_en.txt" to setup.cfg"

This reverts commit 01f2a328.

Reason: The file list changed in this commit was only for py.test
        to lookup possible test sources (doctests or Python tests).
        Wordlists do not contain tests.

setup.cfg

@@ -6,4 +6,4 @@ docs = develop easy_install diceware[docs]
 [pytest]
 addopts = --doctest-modules
           --doctest-glob='*.rst'
-          tests docs README.rst diceware.py wordlists/wordlist_en.txt
+          tests docs README.rst diceware.py