chore(docsApp): don't display module components if none exist

Some modules (ngMessageFormat, ngParseExt) don't have their own api surface
because they integrate with core services ($interpolate and $parse respectively).

Closes #14770

Author: Narretz

docs/config/templates/api/module.template.html

@@ -69,6 +69,7 @@ <h2 id="known-issues">Known Issues</h2>
 {% endif %}
 
 
+{% if doc.componentGroups.length %}
 <div class="component-breakdown">
   <h2>Module Components</h2>
   {% for componentGroup in doc.componentGroups %}
@@ -89,6 +90,7 @@ <h3 class="component-heading" id="{$ componentGroup.groupType | dashCase $}">{$
   </div>
   {% endfor %}
 </div>
+{% endif %}
 
 {% if doc.usage %}
   <h2>Usage</h2>