Remove useless "No X-KDE-DBus-ServiceName found" message

Summary:
None of the KDED modules provide a X-KDE-DBus-ServiceName, so there are
a lot of warnings during session startup.
Not providing the entry actually is no error, as:

1. modules are loaded and requested using the org.kde.kded5 service
2. org.kde.kded5 already is a singleton, so protecting against multiple

instances of the module is not necessary.

Test Plan: make

Reviewers: Frameworks, davidedmundson

Reviewed By: davidedmundson

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D15842