burs/show: remove BUR update count estimate.

Remove the post update count estimate from BUR show pages. This was
complex, slow, and usually inaccurate since it assumed that requests in
a BUR had no overlap with each other, which usually wasn't the case.

app/models/bulk_update_request.rb

@@ -206,10 +206,6 @@ class BulkUpdateRequest < ApplicationRecord
     status == "rejected"
   end
 
-  def estimate_update_count
-    AliasAndImplicationImporter.new(script, nil).estimate_update_count
-  end
-
   def update_notice
     TagChangeNoticeService.update_cache(
       AliasAndImplicationImporter.new(script, nil).affected_tags,