Removed GroupUser couchapp from ReqMgr unittests

ReqMgr unittests pushing GroupUser couchapp was not necessary, removed. The
couchapp is not used in ReqMgr at all.
Merge pull request #4565 from zdenekmaxa/reqmgr-remove-groupuser-couchapp-references

Removed GroupUser couchapp from ReqMgr unittests