Stop trying to read depfile from vtsc

vtsc just ignores the -d argument and apparently can't write a depfile.
So for now, just stop assuming it produces one.

Bug: 121058584
Bug: 120496070
Test: NINJA_ARGS="-w missingdepfile=err" m libvts_interfacespecification
Change-Id: Ie1483fbeead9f710d8a6636df07ce44bbc4a6e2d