Have master-side SVN steps respect the timeout when removing files and directories

This addresses the issue described at <http://trac.buildbot.net/ticket/3055>.
[That's correct](http://docs.buildbot.net/latest/developer/cls-remotecommands.html#buildbot.process.remotecommand.RemoteCommand.useLog).  Without that call, stdout/stderr/header updates from the command will be ignored on the master.