Removes all our logger wrappers except the wrapper for log4j1.2. If you
depend on Elasticsearch's jar in your application you'll need to declare
log4j 1.2 and/or some bridge to your favorite logger.
We did this to simplify our builds and code. No more commons-logging like
log implementation sniffing. No more optional dependency hacks in gradle.
We might one day want to use j.u.l instead of log4j. If we do want that
we can recover its wrapper by studying this commit. We didn't go directly
to j.u.l in this commit because that is a bigger change. Our logging
configuration is based on log4j1.2 and people are used to it. So it'd
be a much more fraught breaking change to do that conversion.
