Refactor astroquery/utils/system_tools.py

All imports are now done at modul level and unused code has been
removed.

Author: eerovaher

astroquery/utils/system_tools.py

@@ -1,15 +1,8 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
 
+import gzip
 import os
-
-# Import DEVNULL for py3 or py3
-try:
-    from subprocess import DEVNULL
-except ImportError:
-    DEVNULL = open(os.devnull, 'wb')
-
-# Check availability of some system tools
-# Exceptions are raised if not found
+import shutil
 
 
 def gunzip(filename):
@@ -19,17 +12,13 @@ def gunzip(filename):
     ----------
     filename : str
         Fully qualified path of the file to decompress.
+
     Returns
     -------
     filename : str
         Name of the decompressed file (or input filename if gzip is not
         available).
     """
-    import shutil
-    import gzip
-
-    # system-wide 'gzip' was removed, Python gzip used instead.
-    # See #1538 : https://github.com/astropy/astroquery/issues/1538
 
     # ".fz" denotes RICE rather than gzip compression
     if not filename.endswith('.fz'):