Revert "[rubygems/rubygems] Remove unneeded teardown"

This reverts commit 0da416ab170dbe1cbd530a5a7c5e8128910014b2.

test/rubygems/test_gem_commands_signout_command.rb

@@ -8,9 +8,15 @@ class TestGemCommandsSignoutCommand < Gem::TestCase
 
   def setup
     super
+
     @cmd = Gem::Commands::SignoutCommand.new
   end
 
+  def teardown
+    super
+    File.delete Gem.configuration.credentials_path if File.exist?(Gem.configuration.credentials_path)
+  end
+
   def test_execute_when_user_is_signed_in
     FileUtils.mkdir_p File.dirname(Gem.configuration.credentials_path)
     FileUtils::touch Gem.configuration.credentials_path