x509: remove subject_base() function

The x509.subject_base() function is only used in tests. During
the recent certificate refactoring, we had to get rid of the
ipalib.x509 import from the module scope so that there were no
circular dependecies and add it exactly to this funcion which
is not used in the production code.

Reviewed-By: Tibor Dudlak <tdudlak@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipalib/x509.py

@@ -51,7 +51,6 @@ from pyasn1_modules import rfc2315, rfc2459
 import six
 
 from ipalib import errors
-from ipapython.dn import DN
 from ipapython.dnsutil import DNSName
 
 if six.PY3:
@@ -76,18 +75,6 @@ EKU_PLACEHOLDER = '1.3.6.1.4.1.3319.6.10.16'
 SAN_UPN = '1.3.6.1.4.1.311.20.2.3'
 SAN_KRB5PRINCIPALNAME = '1.3.6.1.5.2.2'
 
-_subject_base = None
-
-def subject_base():
-    from ipalib import api
-    global _subject_base
-
-    if _subject_base is None:
-        config = api.Command['config_show']()['result']
-        _subject_base = DN(config['ipacertificatesubjectbase'][0])
-
-    return _subject_base
-
 
 @crypto_utils.register_interface(crypto_x509.Certificate)
 class IPACertificate(object):