sd-stub: drop any support for TPM 1.2

sd-stub: drop any support for TPM 1.2

TPM 1.2 is obsolete, and doesn't really provide much security guarantees
given it's build around SHA1 which is not up to today's standards.

The rest of systemd's TPM codebase never supported TPM 1.2 hence let's
drop this partial support in sd-stub too. It has created problems after
all (sd-stub reported the measuements and userspace assumed these were
for TPM2), without bringing any benefits (given that the measurements we
make are not consumed by us anyway, unlike those for TPM 2.0)

let's cut off this old support.