This reverts commit ba2c8d95ec.
This commit introduced some bugs (it used Pattern[Union[str, unicode]]
when it would need to be Union[Pattern[str], Pattern[unicode]]), and
- on further discussion - it's unclear if we want to allow this
additional flexibility. I'm reverting this diff for now, but we'll
revisit this after deciding on the upcoming proposal about how implicit
bytes/unicode conversions should be handled when typing Python 2.
David Fisher