[mobile/wifi] Improve connection removal drawer

Summary:
The code was overly complex and produced a few warnings.
The appearance mostly stays the same, except the drawer isn't as high as before

Test Plan:
Before:

After:

The weird drawer placement seems to be an unrelated issue

Reviewers: Plasma, VDG, jgrulich

Reviewed By: jgrulich

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D22184