UI: Clean up disabling simpleFlvTracks

Since this widget is disabled every time it's shown and we're not
enabling this anywhere, it can just be disabled in the UI form.

UI/forms/OBSBasicSettings.ui

@@ -2048,6 +2048,9 @@
                           </layout>
                          </widget>
                          <widget class="QWidget" name="simpleFlvTracks">
+                          <property name="enabled">
+                           <bool>false</bool>
+                          </property>
                           <layout class="QHBoxLayout" name="horizontalLayoutSimpleFLVTracks">
                            <property name="leftMargin">
                             <number>0</number>

UI/window-basic-settings.cpp

@@ -5902,14 +5902,12 @@ void OBSBasicSettings::SimpleRecordingEncoderChanged()
 
 	if (qual == "Stream") {
 		ui->simpleRecTrackWidget->setCurrentWidget(ui->simpleFlvTracks);
-		ui->simpleFlvTracks->setEnabled(false);
 	} else if (qual == "Lossless") {
 		ui->simpleRecTrackWidget->setCurrentWidget(ui->simpleRecTracks);
 	} else {
 		if (format == "flv") {
 			ui->simpleRecTrackWidget->setCurrentWidget(
 				ui->simpleFlvTracks);
-			ui->simpleFlvTracks->setEnabled(false);
 		} else {
 			ui->simpleRecTrackWidget->setCurrentWidget(
 				ui->simpleRecTracks);