* lib/set.rb (Set#delete_if, Set#keep_if): Avoid blockless call of
  proc, which is not portable to JRuby.  Replace &method() with
  faster and simpler literal blocks while at it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40857 b2dd03c8-39d4-4d8f-98ff-823fe69b080e