sdk: Kill TelephonyExtUtils class

Since Android 10 arrived, the support for manual SIM provisioning
was never ported. In fact, there seems to be a way to do that
using some bits of AOSP code.

This way we get rid of the telephony-ext dependency for good.

Change-Id: Ibe4e430d696782032b7d9840ab36db040c3a4df9