detach cancelled subscribers from VLR

When a subscriber is cancelled, fake an IMSI detach to
ensure that the subscriber gets removed from the VLR.

I am not entirely sure if this change is correct but
it does make TTCN3 test MSC_Tests.TC_gsup_cancel pass.

Change-Id: I5918106e4a94ba2e6c61bcd7b90d3bf0565513cc
Related: OS#2886
1 file changed