Remove CFE_ES_FormCDSName and merge it's functionality into CFE_ES_RegisterCDS

[thnkslprpt]

I think this particular function (CFE_ES_FormCDSName) is a broken API, and should be removed (its not public). It is called in just one place - from CFE_ES_RegisterCDS() - and that can just do an snprintf directly. It actually needs to know the app name anyway for an event later on, so this would also avoid getting it twice. A win-win.

Originally posted by @jphickey in #2173 (comment)