output Update 56ae33f for python3

We dropped python2 support in the middle of this work so updating
56ae33f to reflect this. Also remove
duplicate csv import.

Author: michaelwood

flattentool/output.py

@@ -8,16 +8,13 @@
 from openpyxl.cell.cell import ILLEGAL_CHARACTERS_RE
 import csv
 import os
-import sys
 from warnings import warn
 from flattentool.exceptions import DataErrorWarning
 
 from odf.opendocument import OpenDocumentSpreadsheet
 import odf.table
 import odf.text
 
-import csv
-
 
 class SpreadsheetOutput(object):
     # output_name is given a default here, partly to help with tests,
@@ -128,7 +125,7 @@ def write_sheet(self, sheet_name, sheet):
             row = odf.table.TableRow()
             for header in sheet_header:
                 value = sheet_line.get(header)
-                if isinstance(value, six.text_type):
+                if isinstance(value, str):
                     new_value = ILLEGAL_CHARACTERS_RE.sub('', value)
                     if new_value != value:
                         warn("Character(s) in '{}' are not allowed in a spreadsheet cell. Those character(s) will be removed".format(value),