Remove unused CalculateHash utility method.
Remove unused CalculateHash utility method.

Usages were removed in revision 3ff2f1eb98.

mnaiman/duplicati,duplicati/duplicati,sitofabi/duplicati,sitofabi/duplicati,duplicati/duplicati,duplicati/duplicati,sitofabi/duplicati,mnaiman/duplicati,sitofabi/duplicati,duplicati/duplicati,sitofabi/duplicati,duplicati/duplicati,mnaiman/duplicati,mnaiman/duplicati,mnaiman/duplicati