Remove support for test patches

[conorsch]

The test patches for Grsecurity have been discontinued: https://grsecurity.net/passing_the_baton.php The only options now are stable and stable2. Update the url-fetching module to omit the test patch type.

[conorsch]

Should be straightforward: since we have other options in the grsecurity_urls.py module already, viz. stable and stable2, we can just remove those and the role will continue to work as expected. Docs need to be updated as well.