qt: fix excessive base heights in simple prefs ui files

Viewing the ui files in Qt creator revealed excess empty space at the
bottom of some, a huge amount in the case of media-library. This ultimately
has no impact upon the final result, but I thought I'd fix it for neatness.

Note that these numbers were the product of simply dragging the canvas size
until it snapped into place.

modules/gui/qt/dialogs/preferences/sprefs_audio.ui

@@ -8,7 +8,7 @@
     <x>0</x>
     <y>0</y>
     <width>707</width>
-    <height>626</height>
+    <height>572</height>
    </rect>
   </property>
   <property name="sizePolicy">

modules/gui/qt/dialogs/preferences/sprefs_input.ui

@@ -8,7 +8,7 @@
     <x>0</x>
     <y>0</y>
     <width>737</width>
-    <height>631</height>
+    <height>580</height>
    </rect>
   </property>
   <property name="windowTitle">

modules/gui/qt/dialogs/preferences/sprefs_interface.ui

@@ -8,7 +8,7 @@
     <x>0</x>
     <y>0</y>
     <width>700</width>
-    <height>1069</height>
+    <height>808</height>
    </rect>
   </property>
   <property name="sizePolicy">

modules/gui/qt/dialogs/preferences/sprefs_medialibrary.ui

@@ -8,7 +8,7 @@
     <x>0</x>
     <y>0</y>
     <width>700</width>
-    <height>1069</height>
+    <height>507</height>
    </rect>
   </property>
   <property name="sizePolicy">

modules/gui/qt/dialogs/preferences/sprefs_video.ui

@@ -8,7 +8,7 @@
     <x>0</x>
     <y>0</y>
     <width>682</width>
-    <height>679</height>
+    <height>595</height>
    </rect>
   </property>
   <property name="windowTitle">