consolidate all APN stuff to apns.mk

- remove cdma.mk
- remove apns-conf-cdma.xml
- add everything from apns-conf-cdma.xml to apns-conf.xml
- rename gsm.mk to apns.mk since it now has ALL apns
- remove Stk which should now be called in device trees for GSM devices

Change-Id: I46e09657600e32fe79d44bd4a6817f024d44b019