Revert "Add OpenNIC alternative root servers to /etc/default/dnscrypt-proxy."

This reverts commit 52d2c7c38a23be1b017f7b114ef70a7eb5dded24.
Link to resolver lists in /etc/default and note that specifying multiple resolvers is not yet supported
Merge pull request #63 from Shnatsel/fix-etc-defaults

Fix /etc/default in Ubuntu package