Cleaned up HPresolve::removeSlacks but left off by default since not … #2275

Job	Run time
debug (macos-latest)	8m 49s
debug_all_tests (macos-latest)	9m 9s
debug64 (macos-latest)	8m 3s
debug64_all_tests (macos-latest)	8m 6s
release (macos-latest)	6m 10s
Release64 (macos-latest)	5m 54s
release_all_tests (macos-latest)	14m 17s
Release64_all_tests (macos-latest)	6m 43s
	1h 7m 11s

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