Remove EntryDescriptionRegistry

The EntryDescriptionRegistry is a singleton that is used only for reading the provenance in old files written in or after CMSSW_2_1_0 but before CMSSW_3_0_0.  Singletons are bad for the multithreaded framework, so this pull request eliminates this singleton.  In this particular case, the data held by this singleton is not needed outside the input source, so it is relatively easy to eliminate the use of a singleton.