make Sling work without JCR locking

The Oak team is planning to phase out JCR locking (see <https://issues.apache.org/jira/browse/OAK-6421>). This means that at some point the repository will start to throw exceptions when trying to lock nodes, and the repository descriptors will say that locking is not supported.

As part of <https://issues.apache.org/jira/browse/OAK-7458>, we have added logging for lock related calls (see org.apache.jackrabbit.oak.jcr.lock.LockDeprecation) so that we can identify callers.

One early find was:

<https://github.com/apache/sling-org-apache-sling-jcr-contentloader/blob/master/src/main/java/org/apache/sling/jcr/contentloader/internal/ContentLoaderService.java#L321>