drop gPlazma1 config file and options

gPlazma1 has been removed from master both as native code and as plug-in to
gPlazma2.

* Drop the gPlazma1 configuration file dcachesrm-gplazma.policy.
* Mark the options gplazmaPolicy and gplazma.legacy.config as being obsolete.

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>