Pass only column name to `#remove_column`

@mvz caught this in 90ea9dab.
Thank you!

lib/paperclip/schema.rb

@@ -34,7 +34,7 @@ module Paperclip
 
 
         attachment_names.each do |attachment_name|
         attachment_names.each do |attachment_name|
           COLUMNS.each_pair do |column_name, column_type|
           COLUMNS.each_pair do |column_name, column_type|
-            remove_column(table_name, "#{attachment_name}_#{column_name}", column_type)
+            remove_column(table_name, "#{attachment_name}_#{column_name}")
           end
           end
         end
         end
       end
       end