Docs: Remove reference to nonexistent section.
Docs: Remove reference to nonexistent section.

Shamel added this warning about irreversible things not working.
I assume it's related to
https://github.com/ReactionMechanismGenerator/RMG-Py/issues/345

chatelak/RMG-Py,nickvandewiele/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py,pierrelb/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,chatelak/RMG-Py