Subtle issues with building of libss after change to libks2

[xrobau]

When building this manually, it will fail if libks AND libks2 are not installed, when building the tests.

This commit is required to complete creation of the deb: https://github.com/signalwire/libstirshaken/commit/65272ac2f4af05d9e25d04753e2ecbeddb23e6d0

This is hidden because the Dockerfile and do_install.sh both install libks instead of libks2

I suspect that if both of those were updated, the automated builds would fail, until the commit above is merged.