(core) Remaining Python 3 compatibility changes

Summary: Biggest change is turning everything to unicode

Test Plan: The tests

Reviewers: dsagal, paulfitz

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2875

sandbox/grist/testutil.py

@@ -59,7 +59,7 @@ def parse_testscript(script_path=None):
         all_lines.append(line)
   full_text = "".join(all_lines)
 
-  script = byteify(json.loads(full_text))
+  script = json.loads(full_text)
 
   samples = {}
   test_cases = []
@@ -109,16 +109,6 @@ def parse_test_sample(obj, samples={}):
   return {"SCHEMA": schema, "DATA": data}
 
 
-def byteify(data):
-  """
-  Convert all unicode strings in a parsed JSON object into utf8-encoded strings. We deal with
-  utf8-encoded strings throughout the test.
-  """
-  if isinstance(data, unicode):
-    return data.encode('utf-8')
-  return actions.convert_recursive_helper(byteify, data)
-
-
 def replace_nans(data):
   """
   Convert all NaNs and Infinities in the data to descriptive strings, since they cannot be