DEV: Remove the migration specs (#295)

They're no longer useful

spec/db/post_migrate/20210714173022_correctly_move_assignments_from_custom_fields_to_a_table_spec.rb

@@ -1,40 +0,0 @@
-# frozen_string_literal: true
-
-require "rails_helper"
-require_relative "../../../db/post_migrate/20210714173022_correctly_move_assignments_from_custom_fields_to_a_table"
-
-describe CorrectlyMoveAssignmentsFromCustomFieldsToATable do
-  context "valid data" do
-    # TODO: remove all these specs since they're invalid with the updated schema?
-    skip "should migrate the data correctly" do
-      TopicCustomField.create!(topic_id: 99, name: "assigned_to_id", value: "50")
-      TopicCustomField.create!(topic_id: 99, name: "assigned_by_id", value: "60")
-      silence_stdout { CorrectlyMoveAssignmentsFromCustomFieldsToATable.new.up }
-
-      assignment = Assignment.first
-      expect(assignment.topic_id).to eq(99)
-      expect(assignment.assigned_to_id).to eq(50)
-      expect(assignment.assigned_by_user_id).to eq(60)
-      expect(assignment.target_id).to eq(99)
-      expect(assignment.target_type).to eq('Topic')
-    end
-  end
-
-  context "no assigned_by data" do
-    it "should migrate the data correctly" do
-      TopicCustomField.create!(topic_id: 99, name: "assigned_to_id", value: "50")
-      silence_stdout { CorrectlyMoveAssignmentsFromCustomFieldsToATable.new.up }
-
-      expect(Assignment.count).to eq(0)
-    end
-  end
-
-  context "no assigned_to data" do
-    it "should migrate the data correctly" do
-      TopicCustomField.create!(topic_id: 99, name: "assigned_by_id", value: "60")
-      silence_stdout { CorrectlyMoveAssignmentsFromCustomFieldsToATable.new.up }
-
-      expect(Assignment.count).to eq(0)
-    end
-  end
-end