Remove unwanted refs after importing a project

Because we don't need them, and they would slow down
the repository, keeping unneeded objects as well.

We could also consider doing this in regular housekeeping.

app/models/project.rb

@@ -372,7 +372,7 @@ class Project < ActiveRecord::Base
       if Gitlab::ImportSources.importer_names.include?(project.import_type) && project.repo_exists?
         project.run_after_commit do
           begin
-            Projects::HousekeepingService.new(project).execute
+            Projects::ImportExport::CleanupService.new(project).execute
           rescue Projects::HousekeepingService::LeaseTaken => e
             Rails.logger.info("Could not perform housekeeping for project #{project.full_path} (#{project.id}): #{e}")
           end

app/services/projects/housekeeping_service.rb

@@ -26,6 +26,8 @@ module Projects
       lease_uuid = try_obtain_lease
       raise LeaseTaken unless lease_uuid.present?
 
+      yield if block_given?
+
       execute_gitlab_shell_gc(lease_uuid)
     end
 

app/services/projects/import_export/cleanup_service.rb

@@ -0,0 +1,33 @@
+module Projects
+  module ImportExport
+    class CleanupService
+      RESERVED_REFS_REGEXP =
+        %r{\Arefs/(?:heads|tags|merge\-requests|keep\-around|environments)/}
+
+      attr_reader :project
+
+      def initialize(project)
+        @project = project
+      end
+
+      # This could raise Projects::HousekeepingService::LeaseTaken
+      def execute
+        Projects::HousekeepingService.new(project).execute do
+          garbage_refs.each(&rugged.references.method(:delete))
+        end
+      end
+
+      private
+
+      def garbage_refs
+        @garbage_refs ||= rugged.references.reject do |ref|
+          ref.name =~ RESERVED_REFS_REGEXP
+        end
+      end
+
+      def rugged
+        @rugged ||= project.repository.rugged
+      end
+    end
+  end
+end