Revert "Network Settings: move APN to common area, both CDMA and GSM use this"

This reverts commit f09f2f66dccbafea9e5fa5204b443d19181a78e0.

This causes a major crash on MSIM devices. http://pastebin.com/843G93k0
The setting was moved to network_settings.xml but it is still adding the
preferences from gsm_umts_options.xml
src/android/phone/GsmUmtsOptions.java#L64 hence it can't find the settings key.
Not sure how it even works on single sim this way

Change-Id: I91aa160add0cc0352de5e3704d0adcd12dacbd0b