Tests: remove sacrificial_column

This column has been in the test database since Andy's first commit in
2009, but it's purpose is unclear. There was only one test that mentioned
it, but the test involved only AR methods, nothing from PT. We don't
need to test AR, they've got plenty of their own tests.

test/dummy/db/migrate/20110208155312_set_up_test_tables.rb

@@ -32,7 +32,6 @@ def up
       t.time      :a_time
       t.date      :a_date
       t.boolean   :a_boolean
-      t.string    :sacrificial_column
       t.string    :type
       t.timestamps null: true
     end

test/dummy/db/schema.rb

@@ -250,12 +250,11 @@
     t.text     "a_text"
     t.integer  "an_integer"
     t.float    "a_float"
-    t.decimal  "a_decimal",          precision: 6, scale: 4
+    t.decimal  "a_decimal",  precision: 6, scale: 4
     t.datetime "a_datetime"
     t.time     "a_time"
     t.date     "a_date"
     t.boolean  "a_boolean"
-    t.string   "sacrificial_column"
     t.string   "type"
     t.datetime "created_at"
     t.datetime "updated_at"

test/test_helper.rb

@@ -95,7 +95,6 @@ def assert_changes_equal(expected, actual)
 def change_schema
   ActiveRecord::Migration.verbose = false
   ActiveRecord::Schema.define do
-    remove_column :widgets, :sacrificial_column
     add_column :versions, :custom_created_at, :datetime
   end
   ActiveRecord::Migration.verbose = true
@@ -121,7 +120,6 @@ def reset_version_class_column_info!
 def restore_schema
   ActiveRecord::Migration.verbose = false
   ActiveRecord::Schema.define do
-    add_column :widgets, :sacrificial_column, :string
     remove_column :versions, :custom_created_at
   end
   ActiveRecord::Migration.verbose = true

test/unit/model_test.rb

@@ -520,7 +520,6 @@ class HasPaperTrailModelTest < ActiveSupport::TestCase
         change_schema
         Widget.connection.schema_cache.clear!
         Widget.reset_column_information
-        assert_raise(NoMethodError) { Widget.new.sacrificial_column }
         @last = @widget.versions.last
       end