test_array.rb: fix test for r39466

* test/ruby/test_array.rb (test_sample_random): remove adjustment for
  the bug fixed by r39466.  [ruby-core:52779] [Bug #7935]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39470 b2dd03c8-39d4-4d8f-98ff-823fe69b080e