Don't set acceptHoverEvents in DragArea as we don't use them

Test Plan:
Looked for hoverEvent/Leave/Move in code
We still get mouseMove whilst the user is dragging
Checked Widget Explorer (a user of this class) still works

Reviewers: Plasma

Subscribers: plasma-devel, Frameworks

Tags: Plasma, Frameworks

Differential Revision: https://phabricator.kde.org/D4919