Delete unused tip_question_group template

mentoring/templates/html/tip_question_group.html

-<div class="tip-question-group">
-  <strong>
-    To the question <span class="italic">"{{ self.question }}"</span>,
-    {% if submission %}
-      you answered <span class="italic">"{{ submission_display }}"</span>.
-    {% else %}
-      you have not provided an answer.
-    {% endif %}
-  </strong>
-  {% for tip_fragment in tips_fragments %}
-    {{ tip_fragment.body_html|safe }}
-  {% endfor %}
-</div>