remove extract_sub(), add bsc_subscr_find_or_create_by_mi()

Use the new osmo_mobile_identity API to shed some code dup and simplify.
gsm48_paging_extract_mi() is now unused, drop.

(More refactoring to use osmo_mobile_identity follows in subsequent patch.)

Depends: If4f7be606e54cfa1c59084cf169785b1cbda5cf5 (libosmocore)
Change-Id: Id6cccaac64392b737b3bba8f3a22a88009adb23b
diff --git a/TODO-RELEASE b/TODO-RELEASE
index e2fa427..b822f8a 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -11,3 +11,5 @@
 libosmocore	struct gsm0808_diagnostics	Depends on libosmocore > 1.3.0
 libosmocore	gsm0808_diagnostics_octet_location_str()	Depends on libosmocore > 1.3.0
 libosmocore	gsm0808_diagnostics_bit_location_str()	Depends on libosmocore > 1.3.0
+libosmocore	osmo_mobile_identity	Depends on libosmocore > 1.3.0
+osmo-bsc	Mobile Identity Coding	OsmoBSC is stricter in rejecting invalid coding of Mobile Identity IEs