Improve logging of time zone detection (1/2)

This commit improves logging of time zone detection to
reduce the amount of log spam to the persistent (size 15)
local log buffer.

This is intended as change 1 of 2: just tidying things up.

Bug: 138187241
Test: atest com.android.internal.telephony.NitzStateMachineImplTest
Change-Id: Ia8577f27c030f6187de6d8aefa0203b10e92d6f6