Update example disklabel to bigger slice,

Update example disklabel to bigger slice,
using partition sizes from recommendation and
Hammer partition of more realistic size.

Syncronize disklabel64.8 with disklabel.8.
Delete comments on partition `c' from disklabel64.8,
as partition `c' isn't special in disklabel64 label.

Change `M' to `MB' in disklabel64 output for partition sizes,
to make unit more clear.