DOC: Don't mention Py 3 requirement in _parse_roi_file_py3

Because we automatically switch it out for a Python 2 compatible
version, and the docstring is rendered as if it is for the
wrapper parse_roi_file, which supports both python 2 and python 3.

fissa/readimagejrois.py

@@ -285,9 +285,6 @@ def _parse_roi_file_py3(roi_source):
     """
     Parse an individual ImageJ ROI.
 
-    This implementation utilises the read_roi package, which is more robust
-    but only supports Python 3+ and not Python 2.7.
-
     Parameters
     ----------
     roi_source : str or file object
@@ -306,6 +303,9 @@ def _parse_roi_file_py3(roi_source):
     ValueError
         If unable to parse ROI.
     """
+    # This implementation utilises the read_roi package, which is more robust
+    # but only supports Python 3+ and not Python 2.7.
+
     # Use read_roi package to load up the roi as a dictionary
     roi = read_roi.read_roi_file(roi_source)
     # This is a dictionary with a single entry, whose key is the label