maguro: Switch to World APNs list

Remove gsm.mk and don't copy sample APNs file, use the World APNs
list.

Change-Id: I6eec76ea6c9b61ee47d243ce2d9e4abdca34d84c
maguro: inherit from AOSP .mk file

Inherit from aosp_maguro.mk file in cm.mk, since that is the AOSP
standard now.

Change-Id: I3ce58d1995145b8a79784ce8b3eda5da7a3cef68