tests/drivers/can/timing: Remove unused overlays

The native_{posix,sim}_64 boards are not anymore twister
targets, native_{posix,sim}/native/64 are, and those
default to just use the overlays for the non variant
version.
These 2 overlays were not used by anything.
Remove them.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>