Remove unused dict BYTE_MULTIPLIERS

Dict BYTE_MULTIPLIERS in nova/common/utils.py isn't used
anywhere, and nova/openstack/common/strutils.py includes
this dict, So we can use the one in oslo if we need. It's
safe to remove it now.

Change-Id: I6dde9d7edbaa5e1cbdd6790fe427249d4c2d41ab
Merge "Remove unused dict BYTE_MULTIPLIERS"