Delete Python3.6 image generation job
Once Silkaj v0.9 and DuniterPy v1.0 support is behind us.
Silkaj v0.10 and DuniterPy v1.1 are over-seeding their support.
Copies of 3.6 image can stay in the registry.
Once Silkaj v0.9 and DuniterPy v1.0 support is behind us.
Silkaj v0.10 and DuniterPy v1.1 are over-seeding their support.
Copies of 3.6 image can stay in the registry.