svnpubsub: Remove version header that was uninitentionally added in r1490045.

[in tools/server-side/svnpubsub]
* svnpubsub/server.py
  (Client.write_start): Remove version header.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1490326 13f79535-47bb-0310-9956-ffa450edef68