golang: gimport works on Py3

9c61f254 (pygopath: Initial draft) has a "TODO py3 support", probably
because https://stackoverflow.com/a/67692 shows different codes for
Python2 and Python3.

However today we have tox coverage for all Python2.7, Python3.6 and
Python3.7 and everything works including gimport tests.

-> Remove the TODO.

golang/_gopath.py

@@ -89,5 +89,4 @@ def _gimport(name):
 
 
     # https://stackoverflow.com/a/67692
-    # TODO py3 support
     return imp.load_source(modname, modpath)