ConfigDialog: Simplify the previous fix

Geom's intersectWith & friends have nil guards in place since #7664,
so the insane workaround is completely superfluous.

frontend/ui/widget/configdialog.lua

@@ -921,7 +921,6 @@ function ConfigDialog:update()
         config_dialog = self,
     }
 
-    local old_dimen = self.dialog_frame and self.dialog_frame.dimen and self.dialog_frame.dimen:copy() or Geom:new()
     self.dialog_frame = FrameContainer:new{
         background = Blitbuffer.COLOR_WHITE,
         padding_bottom = 0, -- ensured by MenuBar
@@ -938,16 +937,6 @@ function ConfigDialog:update()
         dimen = Screen:getSize(),
         self.dialog_frame,
     }
-
-    -- Ensure we have a sane Geom object *before* paintTo gets called,
-    -- to avoid weirdness in strange race-y SwipeCloseMenu calls...
-    local dialog_size = self.dialog_frame:getSize()
-    self.dialog_frame.dimen = Geom:new{
-        x = old_dimen.x,
-        y = old_dimen.y,
-        w = dialog_size.w,
-        h = dialog_size.h
-    }
 end
 
 function ConfigDialog:onCloseWidget()