Remove sponsorship level from view and test

app/views/conference/_sponsors.html.haml

@@ -4,16 +4,14 @@
 
 .container
   .row
-    .col-md-12
+    .col-md-12.text-center
       %h2 Sponsors
   - @conference.sponsorship_levels.each do |sponsorship_level|
     -if sponsorship_level.sponsors.any?
-      %h4
-        = sponsorship_level.title
       - sponsorship_level.sponsors.each_slice(3) do |slice|
-        .row
+        .row.row-centered
           - slice.each do |sponsor|
-            .col-md-4.col-sm-4.col-top
+            .col-md-4.col-sm-4.col-centered.col-top
               %a{ href: '#', data: { toggle: 'modal', target: "#modal_#{sponsor.id}" } }
                 = image_tag get_logo(sponsor), class: "img-responsive img-sponsor img-sponsor-#{sponsorship_level.position}"
 
@@ -41,4 +39,3 @@
             Want to sponsor #{@conference.short_title}?
             = link_to("mailto: #{@conference.contact.sponsor_email}?subject=#{@conference.short_title}%20Sponsorship") do
               Please contact us!
-