Remove 'not found in _includes' hacks

Remove the use if "unless contains 'not found in _includes directory'"
hacks that were previously used to detect when _includes were missing.

This change is required as the hack no longer works with the latest
Jekyll release (and therefore also with GitHub).

Additional 'custom_pom_template' and 'custom_gradle_template' flags
must now be set in _config.yml if you want to include a custom pom.xml
or build.gradle file.

_includes/project_sidebar.html

@@ -1,11 +1,9 @@
 {% include documentation.html %}
-{%unless badges contains 'not found in _includes directory' %}
 <div class="right-pane-widget--container no-top-border">
     <div class="project-sub-link--wrapper">
         {% include badges.html %}
     </div>
 </div>
-{%endunless%}
 <div class="right-pane-widget--container no-top-border project-sidebar-resource--wrapper">
     {{ related_resources | markdownify }}
 </div>