dirdiff: Move overlay scrolling disablement into builder file

Author: kaiw

data/ui/filediff.ui

@@ -544,6 +544,7 @@
                     <property name="vexpand">True</property>
                     <property name="hexpand">True</property>
                     <property name="vscrollbar_policy">always</property>
+                    <property name="overlay-scrolling">False</property>
                     <property name="window_placement">top-right</property>
                     <property name="window_placement_set">True</property>
                     <signal name="size-allocate" handler="on_scrolledwindow_size_allocate" swapped="no"/>
@@ -594,6 +595,7 @@
                     <property name="vexpand">True</property>
                     <property name="hexpand">True</property>
                     <property name="vscrollbar_policy">always</property>
+                    <property name="overlay-scrolling">False</property>
                     <signal name="size-allocate" handler="on_scrolledwindow_size_allocate" swapped="no"/>
                     <child>
                       <object class="MeldSourceView" id="textview2">
@@ -642,6 +644,7 @@
                     <property name="vexpand">True</property>
                     <property name="hexpand">True</property>
                     <property name="vscrollbar_policy">always</property>
+                    <property name="overlay-scrolling">False</property>
                     <signal name="size-allocate" handler="on_scrolledwindow_size_allocate" swapped="no"/>
                     <child>
                       <object class="MeldSourceView" id="textview1">

meld/dirdiff.py

@@ -420,9 +420,6 @@ def __init__(self, num_panes):
                 "value-changed", self._sync_vscroll)
             self.scrolledwindow[i].get_hadjustment().connect(
                 "value-changed", self._sync_hscroll)
-            # Revert overlay scrolling that messes with widget interactivity
-            if hasattr(self.scrolledwindow[i], 'set_overlay_scrolling'):
-                self.scrolledwindow[i].set_overlay_scrolling(False)
         self.linediffs = [[], []]
 
         self.update_treeview_columns(settings, 'folder-columns')