Don't set the implicitWidth the parent's actual width
Don't set the implicitWidth the parent's actual width

Summary:
Constrainting the delegate's width to the list view's width makes sense
and will happens automatically.

Constaining the implicitWidth makes no semantic sense.
It throws away an important piece of information and achieves nothing.

Reviewers: #plasma

Differential Revision: https://phabricator.kde.org/D1697

bearsh/kirigami,bearsh/kirigami