Fix warning regarding blur setting

Summary:
There's a bunch of code referring to this setting but not such a setting,
so the qml engine is confused and outputs tons of warnings

Reviewers: #plasma, guoyunhe, ngraham, broulik

Reviewed By: #plasma, broulik

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D8807