[SPARK-20421][CORE] Mark internal listeners as deprecated.

These listeners weren't really meant for external consumption, but they're
public and marked with DeveloperApi. Adding the deprecated tag warns people
that they may soon go away (as they will as part of the work for SPARK-18085).

Note that not all types made public by https://github.com/apache/spark/pull/648
are being deprecated. Some remaining types are still exposed through the
SparkListener API.

Also note the text for StorageStatus is a tiny bit different, since I'm not
so sure I'll be able to remove it. But the effect for the users should be the
same (they should stop trying to use it).

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #17766 from vanzin/SPARK-20421.