Remove uses of sys.exc_info()[1]

Using sys.exc_info()[1] is a hack that was used to use a shared
source approach to Python 3.x support that also included versions
of Python that didn't include the except ... as exc: construction.
Pip no longer supports any of these versions of Python so we can
remove it.
Merge pull request #1508 from dstufft/remove-exception-cruft

Remove uses of sys.exc_info()[1]