Telephony: simplify apns-conf.xml loading logic

Previously, the timestamps of system/etc/apns-conf.xml,
oem/telephony/apns-conf.xml and data/misc/apns/apns-conf.xml
are compared and the newerest one is picked.
However, in release build, all of them will have the
same time stamps, and the system/etc/apns-conf.xml will
always be picked.

This cl will just pick the apns-conf.xml in the following
priority:
data/misc/apns/apns-conf.xml if exists,
oem/telephony/apns-conf.xml if exists
and system/etc/apns-conf.xml (this should always exist)

The impact of this cl is very small as most sane configuration
will have valid system/etc/apns-conf.xml.

BUG: 79584197
Change-Id: Icafa0195cae283910734851cad90a8add4aeeb74
1 file changed