OAK-702: Optimize access to node type information

Use the internal Tree insteance instead of NodeImpl for the
getDefinition() call in internalSetProperty(). Avoid the extra
check on whether a property already exists (see also JCR-3543).

Remove the now unused DefinitionProvider method signature.
Also remove the OAK-652 feature flag as we're getting closer to
resolving the issue.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1461058 13f79535-47bb-0310-9956-ffa450edef68