tdf#136945 use ListStore instead of TreeStore to avoid dnd creating subnodes

because this just wants a flat list and a drop "on" a row shouldn't
create a child of that row, but a sibling

Change-Id: I0a6b360ffe13018d6878bd4bc3012ee3f5807a1a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/124589
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/sd/uiconfig/simpress/ui/definecustomslideshow.ui b/sd/uiconfig/simpress/ui/definecustomslideshow.ui
index fd35ce5..9d8023e 100644
--- a/sd/uiconfig/simpress/ui/definecustomslideshow.ui
+++ b/sd/uiconfig/simpress/ui/definecustomslideshow.ui
@@ -2,7 +2,7 @@
<!-- Generated with glade 3.36.0 -->
<interface domain="sd">
  <requires lib="gtk+" version="3.20"/>
  <object class="GtkTreeStore" id="liststore1">
  <object class="GtkListStore" id="liststore1">
    <columns>
      <!-- column-name text -->
      <column type="gchararray"/>
@@ -10,7 +10,7 @@
      <column type="gchararray"/>
    </columns>
  </object>
  <object class="GtkTreeStore" id="liststore2">
  <object class="GtkListStore" id="liststore2">
    <columns>
      <!-- column-name text -->
      <column type="gchararray"/>