Revert "Fix a Py3 compatability issue with WebTest > 1.3.1 < 2.0"

This reverts commit 9ce0a79866fc4aee0b0988b5b75ce2432c97d0ee.

This was originally an attempted workaround for:
https://github.com/Pylons/webtest/commit/38137ee4b4afb300ab1a8bbf13f66e1a8238b1b8#diff-f8658b710075968677d52c7d013ec098R240
but is an inappropriate fix (that causes a bug of its own).

Change-Id: I3f957a0fff1985596974f51fa154f5de652dc7c5
Merge "Revert "Fix a Py3 compatability issue with WebTest > 1.3.1 < 2.0""