Android build: Clean assets folder before building package

Otherwise deleted files from the project remain in the built .apk archive.

template/android/template.build.xml

@@ -62,9 +62,10 @@
        If this is not done in place, override ${out.dex.input.absolute.dir} */
        -->
     <target name="-post-compile">
-        <copy todir="assets/res">
-            <fileset dir="../res" />
-        </copy>
+    	<delete dir="assets/res"/>
+        <copy todir="assets/res">
+            <fileset dir="../res" />
+        </copy>
     </target>
 
     <!-- Import the actual build file.