impurecord.c: corrected small bug in remove_impucontact_from_list()

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#### Type Of Change - [x] Small bug fix (non-breaking change which fixes an issue) - [ ] New feature (non-breaking change which adds new functionality) - [ ] Breaking change (fix or feature that would change existing functionality)

#### Checklist: <!-- Go over all points below, and after creating the PR, tick the checkboxes that apply --> - [x] PR should be backported to stable branches - [x] Tested changes locally against Version 5.1.0 - [ ] Related to issue #XXXX (replace XXXX with an open issue number)

#### Description <!-- Describe your changes in detail -->

This is the branch 5.1 pull request, created by cherry-pick from https://github.com/kamailio/kamailio/pull/1562 You can view, comment on, or merge this pull request online at:

https://github.com/kamailio/kamailio/pull/1572

-- Commit Summary --

* ims_usrloc_scscf:bugfix erraneous unlinking of deleted contact

-- File Changes --

M src/modules/ims_usrloc_scscf/impurecord.c (3)

-- Patch Links --

https://github.com/kamailio/kamailio/pull/1572.patch https://github.com/kamailio/kamailio/pull/1572.diff