Replace .activity-filter-block with display properties

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

app/assets/stylesheets/framework/mobile.scss

@@ -52,8 +52,4 @@
       padding: 19px 10px;
     }
   }
-
-  .activity-filter-block {
-    display: none;
-  }
 }

app/views/projects/_activity.html.haml

 %div{ class: container_class }
-  .nav-block.activity-filter-block.activities
+  .nav-block.d-none.d-sm-block.activities
     = render 'shared/event_filter'
     .controls
       = link_to project_path(@project, rss_url_options), title: s_("ProjectActivityRSS|Subscribe"), class: 'btn rss-btn has-tooltip' do