Check non-pressure-dependent reactions for uniqueness before core/edge addition.
Check non-pressure-dependent reactions for uniqueness before core/edge addition.

Without this check we were seeing duplicate reactions in the model core
and edge. (The check was removed several commits ago to enable proper
handling of pressure dependence, when it instead should have been moved
to apply to non-pressure-dependent reactions only.

KEHANG/RMG-Py,nickvandewiele/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py,enochd/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,pierrelb/RMG-Py,faribas/RMG-Py,chatelak/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py,enochd/RMG-Py,nyee/RMG-Py,faribas/RMG-Py