[proof] [sat] Fix lost reference to reason when processing redundant literals (#7108)

[proof] [sat] Fix lost reference to reason when processing redundant literals (#7108)

Similarly to the issue when explaining literals, it's necassary to save the
reference to the reason for propagating a redundant literal, as adding
explanations that may be added to the SAT solver during the recursive
elimination of redundant literals may change the original reference.