Homework from 7/10 David lecture.

* Clean unused items from TER.
* Tiny shared_ptr optimization for LES accessor.
Um, do the numeric values of these enums ever make their way into storage or the network?  Even if we only store the string value of the error code, what happens if we read an ancient ledger that contains an error code that is no longer in this file?  If neither of those are issues, then I'm great with this change.  I'm hoping more knowledgeable folks will have the answers.