Merge branch 'fix/remove-legacy-ci-static-model' into 'master'

Remove legacy Ci::StaticModel we do not use anymore

## What does this MR do?

This removes class that according to our code coverage report and
`grep` is a legacy and unused class.

See merge request !5710

lib/ci/static_model.rb

-# Provides an ActiveRecord-like interface to a model whose data is not persisted to a database.
-module Ci
-  module StaticModel
-    extend ActiveSupport::Concern
-
-    module ClassMethods
-      # Used by ActiveRecord's polymorphic association to set object_id
-      def primary_key
-        'id'
-      end
-
-      # Used by ActiveRecord's polymorphic association to set object_type
-      def base_class
-        self
-      end
-    end
-
-    # Used by AR for fetching attributes
-    #
-    # Pass it along if we respond to it.
-    def [](key)
-      send(key) if respond_to?(key)
-    end
-
-    def to_param
-      id
-    end
-
-    def new_record?
-      false
-    end
-
-    def persisted?
-      false
-    end
-
-    def destroyed?
-      false
-    end
-
-    def ==(other)
-      if other.is_a? ::Ci::StaticModel
-        id == other.id
-      else
-        super
-      end
-    end
-  end
-end