Trim leading - from objective bullet points

We already have a checkbox acting as a bullet point, we don't need an
additional `-` which is an artifact of being a markdown bulleted list.

common-theme/layouts/partials/objectives/block.html

@@ -1,8 +1,8 @@
 <ul class="c-objectives__list">
   {{ range . }}
     <li class="c-objectives__item">
-      <label><input type="checkbox" />{{ . }}</label>
+      <label><input type="checkbox" />{{ strings.TrimPrefix "- " . }}</label>
     </li>
   {{ end }}
 </ul>
-<div id="announcer" aria-live="polite"></div>
+<div id="announcer" aria-live="polite"></div>