dbscripts: Remove obsolete integrity-check.{service,timer}

They haven't been used for over 7 years[1] and was just removed from
dbscripts[2][3].

[1] bcd20f65 ("Disable the integrity check timer and service.")
[2] dbscripts!58
[3] f354ae35 ("dbscripts: Bump to latest commit for repos/archive split fixes")