sat-solver: Add a comment on SetActivity().
sat-solver: Add a comment on SetActivity().

It damages the performance, apparently without adding value.
Comment it out.

It is not in the API of Minisat 2.2 (a similar function is for an internal
use), so maybe it should be removed.

opencog/link-grammar,ampli/link-grammar,MadBomber/link-grammar,linas/link-grammar,MadBomber/link-grammar,ampli/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,opencog/link-grammar,opencog/link-grammar,opencog/link-grammar,ampli/link-grammar,ampli/link-grammar,linas/link-grammar,linas/link-grammar,opencog/link-grammar,MadBomber/link-grammar,linas/link-grammar,MadBomber/link-grammar,opencog/link-grammar,linas/link-grammar,opencog/link-grammar,linas/link-grammar,ampli/link-grammar,ampli/link-grammar,MadBomber/link-grammar,MadBomber/link-grammar,ampli/link-grammar,MadBomber/link-grammar,ampli/link-grammar,linas/link-grammar,MadBomber/link-grammar,ampli/link-grammar,linas/link-grammar