output writers: remove the state parameters from writeInit()

because as discussed with Atgeirr, this function should no longer
write the initial solution, it also does no longer need to know the
initial simulator state...
EclipseWriter: fold the writeSolution_() method back into writeTimeStep()

because this was the only caller...
EclipseWriter: remove unused method activeToGlobalCellData_()
Merge pull request #558 from andlaus/EclipseWriter_refactor_writeInit_semantics

Eclipse writer refactor write init semantics