mem: Remove units from stats description

mem: Remove units from stats description

The change https://gem5-review.googlesource.com/c/public/gem5/+/40622
allows units to be shown in stats dump, the units in stats
descriptions are nolonger necessary. This change removes units
from stats descriptions. However, for units that are multiples
of a supported unit (e.g. MegaBytes), the units in the descriptions
are kept until unit prefixes are supported.

Change-Id: I4d87139290a8458e87da776e4328edbd6c224546
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40655
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>