Clean up usage of CountryDetector in PhoneNumberUtils

PhoneNumberUtils calls CountryDetector methods to ascertain whether a
number is an emergency number in the current country, but recent
emergency number detection changes have made the country an unused
parameter. Remove calls to CountryDetector to satisfy mainline
requirements wrt hidden APIs.

Fixes: 148087591
Test: atest PhoneNumberUtilsTest
Change-Id: Ib6ef6348cb1c50e89e24f4f67de6ce76d87550cd