Previously, we would use the CrackSurfaceAssembler class to assemble
the linear term of the crack surface density functional that appears
in the AT-1 model, and then throw it away.  The actual computation
would get the term from the DamagedElasticEnergyDensity implementations.

However, conceptually that linear term doesn't really have anything
to do the the damaged elastic energy density.  Therefore, as a
cleanup measure, remove the AT-1 term from the damaged elastic energy
density implementations.