Remove back link arguments to page footer

We’ve stopped using them in favour of putting any ‘back’ link at the top
of the page. This commit removes them from the macro to make sure we
don’t accidentally reintroduce them.

app/assets/stylesheets/components/page-footer.scss

@@ -3,20 +3,6 @@
   position: relative;
   margin-bottom: 30px;
 
-  &-back-link {
-
-    @include button($grey-1);
-    display: inline-block;
-
-    @include media('mobile') {
-      box-sizing: border-box;
-      width: 100%;
-      margin-top: $gutter-half;
-      text-align: center;
-    }
-
-  }
-
   &-delete-link {
 
     line-height: 40px;

app/templates/components/page-footer.html

@@ -3,8 +3,6 @@
   button_name=None,
   button_value=None,
   destructive=False,
-  back_link=False,
-  back_link_text="Back",
   secondary_link=False,
   secondary_link_text=None,
   delete_link=False,
@@ -22,9 +20,6 @@
         {{- button_text -}}
       </button>
     {% endif %}
-    {% if back_link %}
-      <a class="page-footer-back-link" href="{{ back_link }}">{{ back_link_text }}</a>
-    {% endif %}
     {% if delete_link %}
       <span class="page-footer-delete-link {% if not button_text %}page-footer-delete-link-without-button{% endif %}">
         <a href="{{ delete_link }}">{{ delete_link_text }}</a>