Remove the fragment size, block size, and cpg fields from the disklabel

Remove the fragment size, block size, and cpg fields from the disklabel
program.  disklabel no longer displays these fields and will zero them out
when writing the label back.  newfs and fsck no longer attempt to retrieve
this information from the disklabel.

Replace the obsolete cylinder range and alignment comments with a comment
that displays the size of a partition in megabytes.