Removed platform check that always had the same result

The UM.Application.platform property has been removed by someone for quite some time.
I don't know why the check was in there, but it doesn't seem needed at all as the property was always undefined

plugins/Toolbox/resources/qml/ToolboxConfirmUninstallResetDialog.qml

@@ -26,7 +26,7 @@ UM.Dialog
     minimumWidth: 450 * screenScaleFactor
     minimumHeight: 150 * screenScaleFactor
 
-    modality: UM.Application.platform == "linux" ? Qt.NonModal : Qt.WindowModal
+    modality: Qt.WindowModal
 
     Column
     {

resources/qml/Cura.qml

@@ -563,7 +563,7 @@ UM.MainWindow
 
         //: File open dialog title
         title: catalog.i18nc("@title:window","Open file(s)")
-        modality: UM.Application.platform == "linux" ? Qt.NonModal : Qt.WindowModal;
+        modality: Qt.WindowModal
         selectMultiple: true
         nameFilters: UM.MeshFileHandler.supportedReadFileTypes;
         folder: CuraApplication.getDefaultPath("dialog_load_path")

resources/qml/Dialogs/AskOpenAsProjectOrModelsDialog.qml

@@ -26,7 +26,7 @@ UM.Dialog
     minimumHeight: maximumHeight
     minimumWidth: maximumWidth
 
-    modality: UM.Application.platform == "linux" ? Qt.NonModal : Qt.WindowModal
+    modality: Qt.WindowModal
 
     property var fileUrl
 

resources/qml/Dialogs/OpenFilesIncludingProjectsDialog.qml

@@ -25,7 +25,7 @@ UM.Dialog
     minimumHeight: height
     minimumWidth: width
 
-    modality: UM.Application.platform == "linux" ? Qt.NonModal : Qt.WindowModal;
+    modality: Qt.WindowModal
 
     property var fileUrls: []
     property int spacerHeight: 10 * screenScaleFactor