Disable starting kactivitymanagerd throughout launchertasksmodeltest
Summary:
Currently kactivitymanagerd is loaded halfway through this test, which
has the net result of just breaking.
The test doesn't need it and still passes without it.
Test Plan:
Ran the unit test that's been failing on CI for ages.
It used to fail locally (if run in a new session, see my email on
plasma-devel)
now it passes.
Reviewers: Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D3229