crash: Point to canonical org.chromium.SessionManagerInterface.xml

The session_manager already had a fully-specified .xml file
describing its DBus API, so toss the one created for use
by crash-reporter.gyp, and point the build to the canonical one.

BUG=None
TEST=build crash-reporter and run unit tests

Change-Id: Id14e1a5a3a2aa7be3caee309c04d85078e43a315
Reviewed-on: https://chromium-review.googlesource.com/267726


Trybot-Ready: Chris Masone <cmasone@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Steve Fung <stevefung@chromium.org>
Commit-Queue: Chris Masone <cmasone@chromium.org>