Remove the AndroidX support library dependency

Summary:
Turns out we don't actually need that, the version checks in the Java code
accomplish the same. More importantly, it doesn't support custom icon
graphics, a feature we need to supply icons from the C++ side rather than
from an Android resource.

Reviewers: nicolasfella

Reviewed By: nicolasfella

Subscribers: apol, nicolasfella, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D18329