Revert "ATT default APN"

This reverts commit 334a58a54900d863ab3f13685c9ba978367762db.

Conflicts:
	d850/d850-vendor-blobs.mk
	d850/proprietary/etc/apns-conf.xml

Change-Id: I0b5b16e6050aa9fe5dda925b1964ba767f650810
Revert "remove apns-conf file"

This reverts commit 3b4a8629edfa383ab7e5cc10c13710306659b4b5.

Conflicts:
	d850/proprietary/etc/apns-conf.xml

Change-Id: Ie3cab1887472fc002b9598f35db1dc960da5484e