javalib.jar is now only used for jars that contain dex files, so
host java libraries are now always called classes.jar. Update
layoutlib's custom rules to match. Also remove built_ext_data,
the classes.jar in built_ext_classes already contains the
resources.
Test: layoutlib-tests
Change-Id: I522d9e3786ad7deeb291c7c1a61ec4b86be03dc2