Revert "upgrade 7z to 7zz (#1005)"

This reverts commit 17c0a73f9f.

kindlecomicconverter/shared.py

@@ -18,6 +18,7 @@
 # PERFORMANCE OF THIS SOFTWARE.
 #
 
+from functools import lru_cache
 import os
 from html.parser import HTMLParser
 import subprocess
@@ -124,6 +125,19 @@ def dependencyCheck(level):
         print('ERROR: ' + ', '.join(missing) + ' is not installed!')
         sys.exit(1)
 
+@lru_cache
+def available_archive_tools():
+    available = []
+
+    for tool in ['tar', '7z', 'unar', 'unrar']:
+        try:
+            subprocess_run([tool], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+            available.append(tool)
+        except (FileNotFoundError, subprocess.CalledProcessError):
+            pass
+    
+    return available
+
 def subprocess_run(command, **kwargs):
     if (os.name == 'nt'):
         kwargs.setdefault('creationflags', subprocess.CREATE_NO_WINDOW)