leakchecker.rb: remove temporary measure

* lib/webrick/utils.rb (WEBrick::Utils::TimeoutHandler#watcher):
  make watcher thread restartable.

* lib/webrick/utils.rb (WEBrick::Utils::TimeoutHandler#terminate):
  new method to terminate watcher thread.

* test/lib/leakchecker.rb (LeakChecker#find_threads): revert
  r46941.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53439 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/net/http/utils.rb

@@ -36,6 +36,7 @@ module TestNetHTTPUtils
     if @server
       @server.shutdown
       @server_thread.join
+      WEBrick::Utils::TimeoutHandler.terminate
     end
     @log_tester.call(@log) if @log_tester
     # resume global state