Set same options for proofs as for unsat cores (#1957)

Set same options for proofs as for unsat cores (#1957)

In SmtEngine::setDefaults() we were setting options such as
--simplifciation=none for unsat cores but not proofs. Producing unsat
cores relies on the same infrastructure as proofs and should be a subset
of the same work in most cases. Thus, this commit changes
SmtEngine::setDefaults() to set the same options for proofs as we
previously only did for unsat cores. Additionally, it changes the
function to only set the simplificationMode to SIMPLIFICATION_MODE_BATCH
if proofs and unsat cores are not enabled. Fixes issue #1953.