Revert "freeze.py: del unused variable"

I now believe this is a mistake, as modifying the output vars
during an os.walk can change its behavior.

This reverts commit 045ce25.

Author: ferdnyc

freeze.py

@@ -130,7 +130,6 @@
 def find_files(directory, patterns):
     """ Recursively find all files in a folder tree """
     for root, dirs, files in os.walk(directory):
-        del dirs  # not used
         for basename in files:
             if ".pyc" not in basename and "__pycache__" not in basename:
                 for pattern in patterns: