Rename 'throwaway' variables to single underscore

Also removed unused ones

whipper/program/arc.py

@@ -31,7 +31,7 @@ def accuraterip_checksum(f, track_number, total_tracks, wave=False, v2=False):
     if not wave:
         flac.stdout.close()
 
-    out, err = arc.communicate()
+    out, _ = arc.communicate()
 
     if not wave:
         flac.wait()

whipper/program/cdparanoia.py

@@ -263,7 +263,7 @@ class ReadTrackTask(task.Task):
         stopTrack = 0
         stopOffset = self._stop
 
-        for i, t in enumerate(self._table.tracks):
+        for i, _ in enumerate(self._table.tracks):
             if self._table.getTrackStart(i + 1) <= self._start:
                 startTrack = i + 1
                 startOffset = self._start - self._table.getTrackStart(i + 1)

whipper/program/cdrdao.py

@@ -179,7 +179,7 @@ def version():
     Return cdrdao version as a string.
     """
     cdrdao = Popen(CDRDAO, stderr=PIPE)
-    out, err = cdrdao.communicate()
+    _, err = cdrdao.communicate()
     if cdrdao.returncode != 1:
         logger.warning("cdrdao version detection failed: "
                        "return code is %s", cdrdao.returncode)

whipper/program/sox.py

@@ -18,7 +18,7 @@ def peak_level(track_path):
         logger.warning("SoX peak detection failed: file not found")
         return None
     sox = Popen([SOX, track_path, "-n", "stats", "-b", "16"], stderr=PIPE)
-    out, err = sox.communicate()
+    _, err = sox.communicate()
     if sox.returncode:
         logger.warning("SoX peak detection failed: %s", sox.returncode)
         return None