gnu: torsocks: Upgrade to 2.0.0.

* gnu/packages/tor.scm (torsocks): Update to 2.0.0.
  [source]: Fetch from git.torproject.org.  Use
  'torsocks-dns-test.patch'.
  [arguments, native-inputs]: New fields.
  [license]: Change to GPL2.
* gnu/packages/patches/torsocks-dns-test.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.