top: avoid an unnecessary conversion for 'USED' column

top: avoid an unnecessary conversion for 'USED' column

When the USED column was introduced the proc_t.vm_swap
& proc_t.resident values were added together. However,
using 'resident' required an additional PROC_FILL flag
not to mention extra conversion of pages to kibibytes.

So now we'll use an already present vm_rss value which
removes any special handling for top's derived column.

And while we're at it we'll trade some more 'resident'
field uses with that more immediately usable 'vm_rss'.

Reference(s):
commit 709785e20bd19dc28546d19c45bb7444a56f88b9

Signed-off-by: Jim Warner <james.warner@comcast.net>