BF: make anonymize_script actually output anything and map determinstically

hash() would get a new value for every run for the same sid, so not a good
choice.  Without print script produced no output so code just saw empty
string and assumed that no annonymization was needed etc

Author: yarikoptic

heudiconv/tests/anonymize_script.py

@@ -2,12 +2,12 @@
 
 import sys
 import re
-import ctypes
+import hashlib
 
 
 def bids_id_(sid):
     parsed_id = re.compile(r"^(?:sub-|)(.+)$").search(sid).group(1)
-    return str(ctypes.c_size_t(hash(parsed_id)).value)
+    return hashlib.md5(parsed_id.encode()).hexdigest()[:8]
 
 
 def main():
@@ -16,4 +16,4 @@ def main():
 
 
 if __name__ == '__main__':
-    main()
+    print(main())