Cleanup some Client atmos systems (#33634)

* Cleanup `ScrubberControl.xaml.cs`

* Minor cleanups

* Another pile of minor cleanups

* Apply requested changes

* Rename "which" into "bound". Add whitespace after "if"

Content.Client/Atmos/Monitor/UI/Widgets/ThresholdBoundControl.xaml.cs

@@ -1,7 +1,4 @@
-using Content.Client.Message;
-using Content.Shared.Atmos;
 using Content.Shared.Atmos.Monitor;
-using Content.Shared.Temperature;
 using Robust.Client.AutoGenerated;
 using Robust.Client.UserInterface.Controls;
 using Robust.Client.UserInterface.XAML;