Revert "python.pkgs.blessed: disable failing test"

This reverts commit 4dd38c4289.
Disabling the test suite is unnecessary; I fixed it with
4dd38c4289.

pkgs/development/python-modules/blessed/default.nix

@@ -30,7 +30,7 @@ buildPythonPackage rec {
   checkInputs = [ pytest mock glibcLocales ];
 
   checkPhase = ''
-    LANG=en_US.utf-8 py.test blessed/tests -k 'not test_nested_formattingstring_type_error'
+    LANG=en_US.utf-8 py.test blessed/tests
   '';
 
   propagatedBuildInputs = [ wcwidth six ];