Changes

configure.ac: Remove ibosmo-sccp dependency

osmo-msc had probably forever contained a configure.ac dependency
to libosmo-sccp (that's the old static library libsccp.a), which was
only added to use a single header file (sccp_types.h).  This file
has recently been migrated to libosmo-sigtran, as libsccp.a
has been removed.

Change-Id: Ifcdad8684614c95982b6b471a5585dd42a7fb897