Replace .rss-btn with display properties

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

app/assets/stylesheets/framework/mobile.scss

@@ -20,10 +20,6 @@
     display: none;
   }
 
-  .rss-btn {
-    display: none;
-  }
-
   .container .title {
     padding-left: 15px !important;
   }

app/views/dashboard/_activities.html.haml

 .nav-block.activities
   = render 'shared/event_filter'
   .controls
-    = link_to dashboard_projects_path(rss_url_options), class: 'btn rss-btn has-tooltip', title: 'Subscribe' do
+    = link_to dashboard_projects_path(rss_url_options), class: 'btn d-none d-sm-inline-block has-tooltip', title: 'Subscribe' do
       %i.fa.fa-rss
 
 .content_list

app/views/groups/_activities.html.haml

 .nav-block.activities
   = render 'shared/event_filter'
   .controls
-    = link_to group_path(@group, rss_url_options), class: 'btn rss-btn has-tooltip' , title: 'Subscribe' do
+    = link_to group_path(@group, rss_url_options), class: 'btn d-none d-sm-inline-block has-tooltip' , title: 'Subscribe' do
       %i.fa.fa-rss
 
 .content_list

app/views/projects/_activity.html.haml

@@ -2,7 +2,7 @@
   .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
+      = link_to project_path(@project, rss_url_options), title: s_("ProjectActivityRSS|Subscribe"), class: 'btn d-none d-sm-inline-block has-tooltip' do
         = icon('rss')
 
   .content_list.project-activity{ :"data-href" => activity_project_path(@project) }

app/views/projects/tags/index.html.haml

@@ -27,7 +27,7 @@
       - if can?(current_user, :push_code, @project)
         = link_to new_project_tag_path(@project), class: 'btn btn-success new-tag-btn' do
           = s_('TagsPage|New tag')
-      = link_to project_tags_path(@project, rss_url_options), title: _("Tags feed"), class: 'btn rss-btn has-tooltip' do
+      = link_to project_tags_path(@project, rss_url_options), title: _("Tags feed"), class: 'btn d-none d-sm-inline-block has-tooltip' do
         = icon("rss")
 
   = render_if_exists 'projects/commits/mirror_status'