Remove pointless setMin/setMax size on DesktopView

Summary:
On X, this is entirely useless.There's a special code path in create for
windowType == Desktop and in ::setGeometry it doesn't seem to help/hinder.
It's not like we need WM_NORMAL_HINTS for a WM to resize us.

On wayland it's downright destructive.
On the second setGeometry call the QPA bounds the new geography to the
current min/max (from our previous screenGeometryChanged). But updating
the min/max doesn't update our geometry. End result is our screen is
off.

Test Plan:
Resized screen on Wayland. Wallpaper now filled exactly instead of being broken
Resized screen on Xcb. Wallpaper still filled the screen precisely

Reviewers: Plasma

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D13850