Tidy up use of createHistoryEpoch.
Tidy up use of createHistoryEpoch.

hsorby/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,hsorby/libcellml