cask-tests: remove Travis seed

This hack has been in Homebrew Cask for more than two years
(since 51f93e6dc9c3da4ab2118459ea95e45c104386ec), and it originated even
earlier (6d2f7bc55af0b2aa915b2396d213e30a4446256c).

Cask tests apparently aren't even run on Travis anymore,
so this can be safely removed.

Library/Homebrew/cask/cmd/brew-cask-tests.rb

@@ -19,10 +19,6 @@ repo_root.cd do
   rspec = ARGV.flag?("--rspec") || !ARGV.flag?("--minitest")
   minitest = ARGV.flag?("--minitest") || !ARGV.flag?("--rspec")
 
-  # TODO: setting the --seed here is an ugly temporary hack, to remain only
-  #       until test-suite glitches are fixed.
-  ENV["TESTOPTS"] = "--seed=14830" if ENV["TRAVIS"]
-
   ENV["HOMEBREW_TESTS_COVERAGE"] = "1" if ARGV.flag?("--coverage")
 
   if rspec