Remove link duplication from Community page metadata

[chalin]

Since v0.86.0 of Hugo, render-link hooks are applied to all links, this gives us an opportunity to remove link duplication from the Community card-lists metadata.

For example, consider:

main_channels:
  title: >
      <a href="https://groups.google.com/forum/?hl=en#!forum/etcd-dev" target="_blank" rel="noopener"><i class="fab fa-google"></i>&nbsp;Google Group</a>
  desc: >
      Join the [etcd-dev][] forum to ask questions and get the latest etcd news.

Note that the Google Group link appears in both the title (hard coded) and in the [etcd-dev] link definition -- and this duplication lead to #466 and #481.