pools: remove is_active flag.

Remove uses of the is_active flag. Keep column in database (for now).

The only purpose of this flag was to filter out pools from the pool list
in the Add to Pool dialog. This hasn't had much use since autocomplete
was added. Most pools didn't set the flag correctly anyway.

app/controllers/pool_elements_controller.rb

@@ -21,7 +21,7 @@ class PoolElementsController < ApplicationController
   end
 
   def all_select
-    @pools = Pool.undeleted.where("is_active = true").order("name").select("id, name")
+    @pools = Pool.undeleted.order("name").select("id, name")
     @pools.each # hack to force rails to eager load
     @pools
   end