TEST_MAPPING: don't run vts_libsnapshot_test in kernel-presubmit

libsnapshot test is run in an independent configuration from
kernel-presubmit.  When run in kernel-presubmit, it fails because it
creates another daemon on top of the daemon that is already running from
first stage init.

Bug: 316040872
Test: N/A
Change-Id: Ie3381d6db35bb85fbb47326fa49938416d49f2b8
Signed-off-by: Edward Liaw <edliaw@google.com>