Delete mock_deployment_service model

app/models/project_services/mock_deployment_service.rb

-# frozen_string_literal: true
-
-# Deprecated, to be deleted in 13.8 (https://gitlab.com/gitlab-org/gitlab/-/issues/293914)
-#
-# This was a class used only in development environment but became unusable
-# since DeploymentService was deleted
-class MockDeploymentService < Service
-  default_value_for :category, 'deployment'
-
-  def title
-    'Mock deployment'
-  end
-
-  def description
-    'Mock deployment service'
-  end
-
-  def self.to_param
-    'mock_deployment'
-  end
-
-  # No terminals support
-  def terminals(environment)
-    []
-  end
-
-  def self.supported_events
-    %w()
-  end
-
-  def predefined_variables(project:, environment_name:)
-    []
-  end
-
-  def can_test?
-    false
-  end
-end