Mark emergency dialer package string as untranslatable.

When system language set to XA, config_emergency_dialer_package used to
automatically translate to XA version, which cannot be used by Telecom
to start the emergency dialer.

Bug: 168772316
Test: Manually set system language to XA and make sure emergency dialer
can be start expectedly.

Change-Id: I02a522e0a7dcb871bdebb4e373242d94b7684951