Remove unused CoreEdgeReactionModel.loadSeedMechanism() method.
Remove unused CoreEdgeReactionModel.loadSeedMechanism() method.

I think this stopped being used four years ago in commit 3599f34b550ef7a53ad7081d62b93aa41c44e057
Author: Josh Allen <d2efaa4c3e5af267960de800d4d586f2bce0207f@mit.edu>
Date:   Thu Aug 5 15:32:43 2010 -0400
and is now thoroughly broken. Removing it to reduce confusion.

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