suzerain: #3089 add inst traversal

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suzerain: sg into take_samples

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45112 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: remove slowgrowth::implementation

This extra parameter has gotten unwieldy.  Just admit
that for the foreseeable future all slow growth will
come from Largo and so the formulations are either
enabled or not per largo_formulation.

This change simplifies quite a bit of earlier mess.

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