Remove VtsKernelCheckpointDTFstabTest and have VtsGsiBootTest to take over

The original py test case does not support the usage when there're
disabled dt-fstab nodes. This CL removes the py test and have
VtsGsiBootTest to take over because they share similar logics.

Bug:138449350
Test: run vts -m VtsKernelCheckpointTest on Pixel
Change-Id: I64d1e6f930657d419ab5bac863f0e0fbaf0be9dd
Merged-In: I64d1e6f930657d419ab5bac863f0e0fbaf0be9dd
3 files changed