Adding dun type to Sprint GSM/UMTS APN to use it for tethering.

Without this change tethering does not work when roaming on GSM/UMTS
network. Also removing incorrect/outdated Sprint APNs.

Bug: 23881911
Bug: 24095935
Change-Id: I74a163d171ea7a433977acd5e93dd098f9b7d11d