asterisk-sounds: do not install useless files

Still leave that sounds.xml in there, as I'm not sure what it is for.
And besides, with 5k of plain text size it shouldn't hurt too much if
you already have space for the sounds package. :)

package/asterisk/Makefile

@@ -192,8 +192,11 @@ asterisk-sounds-install:
 	${INSTALL_DIR} $(IDIR_ASTERISK_SOUNDS)/usr/lib/asterisk/sounds
 	$(CP) $(WRKBUILD)/sounds/* \
 		$(IDIR_ASTERISK_SOUNDS)/usr/lib/asterisk/sounds/
-	rm -f $(IDIR_ASTERISK_SOUNDS)/usr/lib/asterisk/sounds/*.mp3
-	rm -f $(IDIR_ASTERISK_SOUNDS)/usr/lib/asterisk/sounds/vm-*
+	(cd $(IDIR_ASTERISK_SOUNDS)/usr/lib/asterisk/sounds; \
+		rm -f *.mp3 vm-*; \
+		rm -f CHANGES* CREDITS* LICENSE* *.txt ; \
+		rm -f *.tar.gz Makefile ; \
+	)
 
 asterisk-voicemail-install:
 	${INSTALL_DIR} $(IDIR_ASTERISK_VOICEMAIL)/etc/asterisk