[Hart] Continue button should not be visible when disabled

Reported that users think the button is broken and don't read
the message above for an explanation of why they can't proceed

Hart request
https://mysocietysupport.freshdesk.com/a/tickets/4818

Surrey request
https://mysocietysupport.freshdesk.com/a/tickets/4768

web/cobrands/fixmystreet/assets.js

@@ -1535,6 +1535,9 @@ fixmystreet.message_controller = (function() {
         if ( $('#js-roads-responsibility').is(':visible') || $('.js-mobile-not-an-asset').length ) {
             return;
         }
+        if (hide_continue_button()) {
+            $('.js-reporting-page--next').show();
+        }
         $('.js-reporting-page--next').prop('disabled', false);
         $("#mob_ok, #toggle-fullscreen").removeClass('hidden-js');
     }
@@ -1546,6 +1549,16 @@ fixmystreet.message_controller = (function() {
             $("#mob_ok, #toggle-fullscreen").addClass('hidden-js');
         } else {
             $('.js-reporting-page--next').prop('disabled', true);
+            if (hide_continue_button()) {
+                $('.js-reporting-page--next').hide();
+            }
+        }
+    }
+
+    function hide_continue_button() {
+        var cobrands_to_hide = ['hart'];
+        if (cobrands_to_hide.indexOf(fixmystreet.cobrand) !== -1) {
+            return 1;
         }
     }