webrick: avoid needless wakeup from IO.select

Since r51231 ("webrick/server.rb: stop immediately"),
there is no need to poll on the @status change every
two seconds.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60144 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/webrick/server.rb

@@ -167,7 +167,7 @@ module WEBrick
           while @status == :Running
             begin
               sp = shutdown_pipe[0]
-              if svrs = IO.select([sp, *@listeners], nil, nil, 2.0)
+              if svrs = IO.select([sp, *@listeners])
                 if svrs[0].include? sp
                   # swallow shutdown pipe
                   buf = String.new