ssconf: Remove unused regular expression

RE_VALID_SSCONF_NAME is not used anywhere.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>

lib/ssconf.py

@@ -27,7 +27,6 @@ configuration data, which is mostly static and available to all nodes.
 """
 
 import sys
-import re
 import os
 import errno
 
@@ -42,8 +41,6 @@ from ganeti import pathutils
 
 SSCONF_LOCK_TIMEOUT = 10
 
-RE_VALID_SSCONF_NAME = re.compile(r"^[-_a-z0-9]+$")
-
 
 class SimpleConfigReader(object):
   """Simple class to read configuration file.