Changes

s1gw: f_ConnHdlr_ue_ctx_release_req(): add a quirk for -latest

We're hitting a crash in Eclipse TITAN when running
S1GW_Tests.TC_uemux_ue_ctx_release_req against the -latest version
of osmo-s1gw, which is sending PFCP Session Deletion Request that
we no longer expect to receive.  This results in an empty junit-xml
file due to early termination of the runtime.

Re-introduce the f_ConnHdlr_session_delete(), only for the -latest.

Change-Id: I90c44955ad3aabfe7ca9198b3ec9b6b97a46c0ae
Related: 8e315ed6 ("s1gw: correct handling of UE CONTEXT RELEASE REQUEST")
Related: osmo-s1gw.git If467162e871b7989f0578be30c04d1c32c263c99
Related: OS#6888, SYS#7738, SYS#7599