Extract @edit[@expkey] to local variable

Changed Flay score on this file FROM:

  4782.3: flog total
   119.6: flog/method average

  2885.4: ApplicationController total
  1017.8: ApplicationController::Filter#exp_changed filter.rb:137
   782.3: ApplicationController::Filter#exp_commit filter.rb:1369
   559.4: ApplicationController::Filter#adv_search_button filter.rb:585
   340.0: ApplicationController::Filter#exp_set_fields filter.rb:1211
   185.9: ApplicationController::Filter#exp_build_string filter.rb:1640

TO:

  3860.2: flog total
    96.5: flog/method average

  2331.8: ApplicationController total
   744.7: ApplicationController::Filter#exp_changed filter.rb:139
   549.8: ApplicationController::Filter#exp_commit filter.rb:1386
   455.2: ApplicationController::Filter#adv_search_button filter.rb:593
   255.6: ApplicationController::Filter#exp_set_fields filter.rb:1226
   185.9: ApplicationController::Filter#exp_build_string filter.rb:1665
   140.5: ApplicationController::Filter#exp_button filter.rb:6