Update logging to use log4cxx, not pex::logging

LSST has recently replaced the custom-written pex::logging with a standard logger, log4cxx.

As of the 12_1 release pex::logging is no longer setup as part of afw, but as there are only two logging statements in all of drp::stella C++ code we may as well convert.

There is no need for backwards compatibility with v12_0 as the ndarray change int -> size_t makes that impossible without a little C++ TMP which doesn't seem worth while (PIPE2D-85)