Remove ReleaseTrack related constants out of DBus.

Get/SetTrack methods have been deprecated. This CL removes their DBus
constants.

BUG=chromium:221850
TEST=Built with https://codereview.chromium.org/21015010

Change-Id: I8294d852e668bc789daeca28a0058ecf0686def4
Reviewed-on: https://gerrit.chromium.org/gerrit/63838
Reviewed-by: Darren Krahn <dkrahn@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
diff --git a/dbus/service_constants.h b/dbus/service_constants.h
index 85e85ad..dca711c 100644
--- a/dbus/service_constants.h
+++ b/dbus/service_constants.h
@@ -1234,9 +1234,7 @@
 // Methods.
 const char kAttemptUpdate[] = "AttemptUpdate";
 const char kGetStatus[] = "GetStatus";
-const char kGetTrack[] = "GetTrack";
 const char kRebootIfNeeded[] = "RebootIfNeeded";
-const char kSetTrack[] = "SetTrack";
 const char kSetChannel[] = "SetChannel";
 const char kGetChannel[] = "GetChannel";