Remove galago from method/variable naming
Summary: With D29021 the fallback notification system is gone and with it the need for differentating naming. Remove galago from the naming since it's outdated and might confuse readers unfamiliar with the code and its history. Also inline a now not needed function.
Still get notifications, action invoked signal is correctly sent
Depends on D29021
Reviewers: Frameworks, broulik
Reviewed By: broulik
Differential Revision: https://phabricator.kde.org/D29336