json_data: Eliminate utf_path

[ferdnyc]

The os.fsencode() conversion and the use of utf_path is causing exceptions when mixing and matching regular expressions applied to utf_path and path:

   json_data:ERROR Error while converting relative paths to absolute paths:
 a bytes-like object is required, not 'str'

path will be a str which is already Unicode, there's no reason to apply conversions.

Also removed the re.UNICODE flag from the regular expression, as it's deprecated and ignored:

Note that for backward compatibility, the re.U flag still exists (as well as its synonym re.UNICODE and its embedded counterpart (?u)), but these are redundant in Python 3 since matches are Unicode by default for strings (and Unicode matching isn’t allowed for bytes).

[ferdnyc]

Turns out this fixes #3094 (who knew?!?), merging.