prebuilt: Update APNs for Boost Mobile

Removed "Boost Mobile CdmaNai" apn as the mmsc domain
mm.myboostmobile.com does not resolve and the only other US network
offered by Boost has a different mmsc
(http://wholesale.mmsmvno.com/mms/wapenc).
https://www.boostmobile.com/support/activation/finish-activation

Change-Id: I203fe6ca705fc2b8eacf954dff843a749bcc6959