Remove an extra quote in no-update-response for v3.0

This was inadvertent and harmless typo and caused a error message about
XML being invalid in update_engine logs. That message should go away
now.

BUG=chromium:224001
TEST=Verified with image to live invalid xml error went away in UE.
Change-Id: Ieab1748e1d8dc2beadff4ddf8086129a50a07e8a
Reviewed-on: https://gerrit.chromium.org/gerrit/46534
Reviewed-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Jay Srinivasan <jaysri@chromium.org>
Tested-by: Jay Srinivasan <jaysri@chromium.org>
Commit-Queue: Jay Srinivasan <jaysri@chromium.org>