filediff, dirdiff: Fix busted overlay scrolling change

The change in 1915de was supposed to just move overlay scrolling
disablement for dirdiff; instead it moved it for filediff and removed
it for dirdiff. This is the other part of the changeset, removing the
lagging code in filediff and actually disabling overlay scrolling in
dirdiff in the UI file.

Author: kaiw

data/ui/dirdiff.ui

@@ -353,6 +353,7 @@
                     <property name="visible">True</property>
                     <property name="can_focus">True</property>
                     <property name="vexpand">True</property>
+                    <property name="overlay-scrolling">False</property>
                     <property name="window_placement">top-right</property>
                     <property name="window_placement_set">True</property>
                     <child>
@@ -411,6 +412,7 @@
                     <property name="visible">True</property>
                     <property name="can_focus">True</property>
                     <property name="vexpand">True</property>
+                    <property name="overlay-scrolling">False</property>
                     <child>
                       <object class="GtkTreeView" id="treeview1">
                         <property name="visible">True</property>
@@ -467,6 +469,7 @@
                     <property name="visible">True</property>
                     <property name="can_focus">True</property>
                     <property name="vexpand">True</property>
+                    <property name="overlay-scrolling">False</property>
                     <child>
                       <object class="GtkTreeView" id="treeview2">
                         <property name="visible">True</property>

meld/filediff.py

@@ -172,9 +172,6 @@ def __init__(self, num_panes):
         for (i, w) in enumerate(self.scrolledwindow):
             w.get_vadjustment().connect("value-changed", self._sync_vscroll, i)
             w.get_hadjustment().connect("value-changed", self._sync_hscroll)
-            # Revert overlay scrolling that messes with widget interactivity
-            if hasattr(w, 'set_overlay_scrolling'):
-                w.set_overlay_scrolling(False)
         self._connect_buffer_handlers()
         self._sync_vscroll_lock = False
         self._sync_hscroll_lock = False