Removed parallel checkpoint test from test_sdp.sh.
This test was done in a way specific to the 2023.2 release when
multi-file parallel checkpoints were new, and before the Battle
School QA Test Suite was in place. Parallel checkpoint functionality
now has far better coverage and is better tested in the Battle School
QA test suite. We can safely drop this old basic test from the
Docker test suite without loss of test coverage.