Remove broken compatibility shim & bare except.
Remove broken compatibility shim & bare except.

Since `io.StringIO` exists in both Python 2 and 3, the removed
try..except statement would never fail.

`cStringIO.StringIO` seems to be faster than `io.StringIO` in Python
2.7, but it doesn't make sense to use it in the interests of
backwards compatiblity.

pydata/conf_site,pydata/conf_site,pydata/conf_site