software/caddy-frontend/test: use lzma directly

We no longer need backports.lzma now this test is python3 only

software/caddy-frontend/test/setup.py

@@ -51,7 +51,6 @@ setup(name=name,
         # caucase needed to connect to the KeDiFa caucase
         'caucase',
         'cryptography',
-        'backports.lzma',
       ],
       zip_safe=True,
       test_suite='test',

software/caddy-frontend/test/test.py

@@ -51,18 +51,13 @@ import urllib.parse
 import socket
 import sys
 import logging
+import lzma
 import random
 import string
 from slapos.slap.standalone import SlapOSNodeInstanceError
 import caucase.client
 import caucase.utils
 
-
-try:
-    import lzma
-except ImportError:
-    from backports import lzma
-
 import datetime
 
 from cryptography import x509