We can remove the following code because @tmp/pdf@ directory that is used when generating pdf files is no longer used after r13358.

Curentry, the PDF library rbpdf uses tmp instead of tmp/pdf as a temporary directory.

diff --git a/lib/redmine/export/pdf.rb b/lib/redmine/export/pdf.rb
index 85beb8bdb..e43459b08 100644
--- a/lib/redmine/export/pdf.rb
+++ b/lib/redmine/export/pdf.rb
@@ -28,8 +28,6 @@ module Redmine
         attr_accessor :footer_date
 
         def initialize(lang, orientation='P')
-          @@k_path_cache = Rails.root.join('tmp', 'pdf')
-          FileUtils.mkdir_p @@k_path_cache unless File::exist?(@@k_path_cache)
           set_language_if_valid lang
           super(orientation, 'mm', 'A4')
           set_print_header(false)