Remove usage of the top-bar-title class

This class was only there in order to use Foundation's styles, but
the amount of styles we were using was equal to the amount of
styles we were overwriting.

app/assets/stylesheets/layout/admin_header.scss

@@ -16,6 +16,7 @@
 
   .top-bar {
     height: auto;
+    padding-bottom: 0;
     padding-top: $line-height / 2;
 
     @include breakpoint(small only) {
@@ -52,7 +53,6 @@
 
     h1 {
       margin-top: $line-height / 2;
-      margin-bottom: 0;
 
       @include breakpoint(medium) {
         margin-top: 0;