Remove state dependence in PBMR400 model

[GiudGiud]

Reason

The pbmr400 transient input now has requires reusing previous state (set snes_reusemf) when we're not sure why that would be. This causes libmesh to complain and request this parameter

Design

Find change in PETSc or Griffin that caused this

Impact

Necessary input modification in the mean time. Slightly higher memory use (it's a cheap model though)