[configview] Simplify code / workaround Qt5.15 crash

Summary:
QQmlComponent::beginCreate and completeCreate are useful if you need to
set properties on the object explicitly. We're not doing that here, we
can just call create.

Test Plan:
On Qt5.15
Right click a panel
choose edit

Reviewers: Plasma, apol

Reviewed By: apol

Subscribers: apol, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D28599