[1120417] Break up transaction of updatePluginConfigurationDefinition into smaller pieces
Another pass here given some oracle test failures in the CI env.
- Fix an issue with PropertyDefinitionSimple.removeEnumeratedValues.
  An unexpected problem brought out, I guess, by the Tx reworking,
  must be careful not to replace hibernate proxy dealing with
  orphanRemoval.
- remove unnecessary REQUIRES_NEW that could lead to locking issues
- remove some dead code
- start shortening xxxInNewTransaction to xxxInNewTx, purely for selfish reasons.
In a recent commit for [1120417] (and the resulting oracle test failures) we
added protection against Hibernate errors related  to detached sets when
orphanRemoval=true.  This applies similar changes to entity classes
outside of the BZ work.