the cassandra migrator does not need to be shard aware

especially when it's flat out wrong and causes it to not work

even when run in a sharded environment, it's run per-shard anyway

Change-Id: I6f568b44a6fe636468372e708cfcdcb329d4a733
Reviewed-on: https://gerrit.instructure.com/46744
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

app/models/page_view.rb

@@ -412,9 +412,7 @@ class PageView < ActiveRecord::Base
     end
 
     def cassandra
-      user.shard.activate do
-        PageView::EventStream.database
-      end
+      PageView::EventStream.database
     end
 
     def run