Don't auto scale outputs where we don't know the physical size

Summary:
We don't have enough data to calculate the DPI properly and the current
code effectively ends up switching based purely on resolution.

CCBUG: 384789

Reviewers: #plasma, fvogt

Reviewed By: fvogt

Subscribers: plasma-devel, fvogt

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D7980