Remove Releases button from News

[hauten]

1. Remove the following lines from the News index.md page when site redesign launches:

• Line 12: <button type="button" class="btn" id="release">Releases</button>
• Line 21: {% increment release %}
• Lines 37-40: beginning with {% elsif page.categories contains "release" and release <= cap %}

2. Remove tag description from pages/news/README.md.

(Note that archive.md will be consolidated with the main news page.)

[hauten]

Confirmed with #647