pylint 2.2: Fix unnecessary pass statement

pylint 2.2.0 has a new checker for unnecessary pass statements. There is
no need to have a pass statement in functions or classes with a doc
string.

Fixes: https://pagure.io/freeipa/issue/7772
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Thomas Woerner <twoerner@redhat.com>

ipapython/certdb.py

@@ -224,19 +224,16 @@ KEY_RE = re.compile(
 class Pkcs12ImportIncorrectPasswordError(RuntimeError):
     """ Raised when import_pkcs12 fails because of a wrong password.
     """
-    pass
 
 
 class Pkcs12ImportOpenError(RuntimeError):
     """ Raised when import_pkcs12 fails trying to open the file.
     """
-    pass
 
 
 class Pkcs12ImportUnknownError(RuntimeError):
     """ Raised when import_pkcs12 fails because of an unknown error.
     """
-    pass
 
 
 class NSSDatabase: