Evaluate need for `set_openmm_threads_1` in simulation tests

[IAlibay]

We now restrict the CPU count in vacuum simulations:

openfe/openfe/protocols/openmm_rfe/equil_rfe_methods.py

Lines 972 to 977 in 9626bbf

	restrict_cpu = forcefield_settings.nonbonded_method.lower() == 'nocutoff'
	platform = omm_compute.get_openmm_platform(
	platform_name=protocol_settings.engine_settings.compute_platform,
	gpu_device_index=protocol_settings.engine_settings.gpu_device_index,
	restrict_cpu_count=restrict_cpu
	)

and

openfe/openfe/protocols/openmm_afe/base.py

Lines 196 to 202 in 9626bbf

	# Restrict CPU count if running vacuum simulation
	restrict_cpu = settings['forcefield_settings'].nonbonded_method.lower() == 'nocutoff'
	platform = omm_compute.get_openmm_platform(
	platform_name=settings['engine_settings'].compute_platform,
	gpu_device_index=settings['engine_settings'].gpu_device_index,
	restrict_cpu_count=restrict_cpu
	)

We shouldn't have to do this in the tests anymore:

openfe/openfe/tests/protocols/test_openmm_rfe_slow.py

Lines 21 to 34 in 9626bbf

	@pytest.fixture
	def set_openmm_threads_1():
	# for vacuum sims, we want to limit threads to one
	# this fixture sets OPENMM_CPU_THREADS='1' for a single test, then reverts to previously held value
	previous: str | None = os.environ.get('OPENMM_CPU_THREADS')
	try:
	os.environ['OPENMM_CPU_THREADS'] = '1'
	yield
	finally:
	if previous is None:
	del os.environ['OPENMM_CPU_THREADS']
	else:
	os.environ['OPENMM_CPU_THREADS'] = previous