Revert "test/rdoc: avoid tempfile leaks"

This reverts commit r46145.

Tempfile.create is only available Ruby 2.1 or higher.
rubygems need to support Ruby 1.9 and 2.0 series.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46683 b2dd03c8-39d4-4d8f-98ff-823fe69b080e