icong: cleanup cm.mk

* gsm.mk doesn't (actually) exist, see:
https://github.com/androidarmv6/android_vendor_cm/blob/cm-11.0/config/gsm.mk
* There's no need for a custom build fingerprint
* Remove weird versioning defines

Change-Id: I5597950b33c1f2a88edbe7bebb393cf1626879ca