Get rid of Google cpplint's warnings about streams.
Get rid of Google cpplint's warnings about streams.

To make the warnings go away, make sure to remove CMake's settings
cache after applying this change.  (Otherwise the old setting of
SURGSIM_CPPLINT_FILTERS will persist.)

simquest/opensurgsim,simquest/opensurgsim,simquest/opensurgsim,simquest/opensurgsim