msc_vlr_test: remove DLMGCP log messages from unit test output

The log output of libosmo-mgcp-client has changed. This change causes
the unit tests to fail because the log output does not match anymore.
Lets disable the DLMGCP log output since it is of minor importance
for VLR testing anyway.

Change-Id: Id197e4ab9ba12e284299ef520edee9c362513bf1
Related: SYS#5091
13 files changed