Do not pull in xtend-lib-osgi

There is no need for the xtend bundle, as yangtools does not rely on
xtend being on classpath anymore. Also eradicate references to xtend
annotation and utility classes.

Change-Id: Iba61200f1af88b4bfd4165d38284d7ddbcac70b5
Signed-off-by: Robert Varga <rovarga@cisco.com>