Merge ~d0ugal/maas-images:lzma into maas-images:master

[Dougal Matthews]

lzma was added to the stdlib in Python 3.3

The backport is no longer needed and removing the try/except shows the
real error if liblzma-dev was missing when Python was compiled.

[Alberto Donato (ack)]

+1

review: Approve

diff --git a/meph2/commands/dpkg.py b/meph2/commands/dpkg.py
index 35ea5eb..e6c1d0e 100644
--- a/meph2/commands/dpkg.py
+++ b/meph2/commands/dpkg.py
@@ -2,6 +2,7 @@ import shutil
 import subprocess
 import hashlib
 import io
+import lzma
 import os
 import re
 import sys
@@ -11,11 +12,6 @@ import glob
 
 from meph2.url_helper import geturl
 
-try:
-    import lzma
-except ImportError:
-    from backports import lzma
-
 # Cache packages
 _packages = {}