emptytest: exclude from world builds

This recipe is for testing purposes and shouldn't be built in world builds, as
it produces errors without being built in the selftest.

(From OE-Core rev: 11fd33dfeea6606494cd0381986523566c03e2eb)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-selftest/recipes-test/emptytest/emptytest.bb

@@ -3,3 +3,5 @@ include test_recipe.inc
 # Set LICENSE to something so that bitbake -p that is ran at the beginning
 # is successful since test_recipe.inc has not yet been modified.
 LICENSE = ""
+
+EXCLUDE_FROM_WORLD = "1"