chore(coderd): remove the window option in open_in (#16104)

As we worked on adding a `open_in` parameter for workspace_apps - we
initially created three options :
- window
- slim_window
- tab

After further investigation, `window` should not be used and has to be
removed.

ℹ️ I decided to remove the option instead of deprecating it as we've not
created any release nor documented the feature. Can be discussed.

provisioner/terraform/resources.go

@@ -437,8 +437,6 @@ func ConvertState(ctx context.Context, modules []*tfjson.StateModule, rawGraph s
 			switch strings.ToLower(attrs.OpenIn) {
 			case "slim-window":
 				openIn = proto.AppOpenIn_SLIM_WINDOW
-			case "window":
-				openIn = proto.AppOpenIn_WINDOW
 			case "tab":
 				openIn = proto.AppOpenIn_TAB
 			}