fix: remove obsolete variable

lib/fotos/organizer.rb

@@ -9,7 +9,6 @@ module Fotos
     end
 
     def call
-      date_format = '%d-%m-%Y'
       source_path_pattern = File.join(@source_path, "**/*")
       paths = Dir.glob(source_path_pattern)
       paths.each do |fp|