Remove xml ui for "region" effect, that does not exist anymore

data/effects/region.xml

-<?xml version="1.0"?>
-<!DOCTYPE kpartgui>
-<effect tag="region" id="region">
-    <name Context="Regionalize Effect Name">Regionalize</name>
-    <description>Apply sub-effects to a region defined by a clip's alpha channel</description>
-    <author>Charles Yates</author>
-    <parameter type="url" name="resource" default="">
-        <name>Url</name>
-    </parameter>
-    <parameter type="geometry" name="composite.geometry" default="0 0:100% 100%" fixed="1" opacity="false">
-        <name>Pan and Zoom</name>
-    </parameter>
-    <parameter type="fixed" name="filter_only" min="1" max="1" default="1"/>
-</effect>