Remove unnecessary condition branch

Remove unnecessary condition branch: the branch will never be used
because:
a) nitzSignal, which is assigned from mLatestNitzSignal, is dereferenced
a few lines above.
b) mLatestNitzSignal is either set or checked before calls to
updateTimeZoneFromCountryAndNitz()

Bug: 140712361
Test: Treehugger only
Change-Id: I8330f8ee8254c1b7875a13535a46e0f5e4bdbc07