ValidationContext: change result caching, use a ThreadLocal

Store the report in the thread local variable, use it to store the report we are
passed as an argument on validation, and get it from the cache validation
function.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
RefResolverProcessor: remove caching

Now that it is done at the validator cache level, there is no need doing it
here.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>