um: remove duplicate UM_NSEC_PER_SEC definition

Just remove the first entry as there is a second later on.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20241103150506.1367695-4-benjamin@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>