Refactor: Remove requirement for local? method

For DRYness. And it removes a tiny bit of required work from the
framework doc.

I was going to write a centralized `local?` method somewhere but
discovered that all `Uploader` classes include `ObjectStorage::Concern`
which implements `file_storage?`, which is an equivalent check to these
`local?` methods.

The `local?` methods are more direct than going through
`replicator.carrierwave_uploader`, but this change is safe because we
already depend on `replicator.carrierwave_uploader` in the
`checksummable?` method.

app/models/packages/package_file.rb

@@ -55,10 +55,6 @@ class Packages::PackageFile < ApplicationRecord
     Gitlab::Routing.url_helpers.download_project_package_file_path(project, self)
   end
 
-  def local?
-    file_store == ::Packages::PackageFileUploader::Store::LOCAL
-  end
-
   private
 
   def update_size_from_file

app/models/terraform/state_version.rb

@@ -17,10 +17,6 @@ module Terraform
     mount_file_store_uploader StateUploader
 
     delegate :project_id, :uuid, to: :terraform_state, allow_nil: true
-
-    def local?
-      file_store == ObjectStorage::Store::LOCAL
-    end
   end
 end
 

doc/development/geo/framework.md

@@ -189,11 +189,6 @@ For example, to add support for files referenced by a `Widget` model with a
 
      mount_uploader :file, WidgetUploader
 
-     def local?
-       # Must to be implemented, Check the uploader's storage types
-       file_store == ObjectStorage::Store::LOCAL
-     end
-
      # @param primary_key_in [Range, Widget] arg to pass to primary_key_in scope
      # @return [ActiveRecord::Relation<Widget>] everything that should be synced to this node, restricted by primary key
      def self.replicables_for_current_secondary(primary_key_in)

ee/app/models/ee/merge_request_diff.rb

@@ -59,8 +59,8 @@ module EE
       super || build_merge_request_diff_detail
     end
 
-    def local?
-      stored_externally? && external_diff_store == ExternalDiffUploader::Store::LOCAL
+    def checksummable?
+      stored_externally? && super
     end
 
     def log_geo_deleted_event

ee/lib/gitlab/geo/replicable_model.rb

@@ -72,14 +72,14 @@ module Gitlab
       #
       # @return [Boolean] whether it can generate a checksum
       def checksummable?
-        local? && file_exist?
+        replicator.carrierwave_uploader.file_storage? && file_exist?
       end
 
       # This checks for existence of the file on storage
       #
       # @return [Boolean] whether the file exists on storage
       def file_exist?
-        if local?
+        if replicator.carrierwave_uploader.file_storage?
           File.exist?(replicator.carrierwave_uploader.path)
         else
           replicator.carrierwave_uploader.exists?