Remove the KeyError catch block in the server (#1130)
Remove the KeyError catch block in the server (#1130)

Several times I've run into an issue where I get a really weird error
message about some key being missing, where there was actually a
`KeyError` deep in my model code that was being caught at this point
and re-branded incorrectly.  I don't think trying to catch the
`KeyError` here is actually useful.
allenai/allennlp,allenai/allennlp,allenai/allennlp,allenai/allennlp