remove dead (?) code, typofix

When fixing some typos I found, I tried to add a test, but I couldn't figure out how to trigger the "Couldn't download distribution" exception, which requires ```Installer._fetch``` to return ```None```.  I can't see that happening, at least with a current ```pkg_resources.Distribution```.

If someone can give me a hint as to when this error would happen, I'd be happy to write a test.  If not, here's a pull request to remove dead code for your consideration.