This reverts commit 4fe2685615.
Always use the preferred_scale requested by the compositor as this
did not work so well in the intended use case (where the low resolution
monitor text was scaled down and difficult to see).
After discussion with @ZedDB, revert this change since there are cases
where either functionality might be preferred - to ensure Blender's UI
is visible on a low resolution mirrored projector for e.g.
Changing the behavior of the preferred scale makes most sense in the
compositor, instead of controlling it on a per-application basis.
0a270e3513