[UWS] Fix HTTP request for job destruction.

Until now, it was possible to destroy the job by posting ACTION=DELETE
with a URL like below:

    {root-uws}/{job-list}/{job-id}/foo/bar

That is completely wrong. The correct URL for this action must always be:

    {root-uws}/{job-list}/{job-id}

This commit fixes this error in UWSServlet and UWSService.