Thread is always provided at current ruby version.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63700 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/sync.rb

@@ -38,10 +38,6 @@
 #
 #
 
-unless defined? Thread
-  raise "Thread not available for this ruby interpreter"
-end
-
 ##
 # A module that provides a two-phase lock with a counter.