Resolve "this last check is only necessary if we do full verification (2/3)" comment

[greg-szabo]

TODO: this last check is only necessary if we do full verification (2/3) but the
above checks should actually happen always (even if we skip forward)

The above comment was introduced lite_impl/signed_header.rs during the Tendermint v0.33 upgrade in this PR

During the code review, it was pointed out that it should go somewhere else.
Anton also commented on it here.

During the CommitSig refactor it came up again so I opened this issue to track it and eventually get rid of it for good.

[brapse]

Although this references a lot of context it is unclear how actionable this is. Can we please update the description to be a context free description of what the actual problem is and how it can be remedied?

[ebuchman]

This comment is in the lite_impl module which will be deprecated/deduplicated ala #342. This kind of issue (ie. checks in full verification that arent in the overlap/bisection verification) will be ultimately dealt with by #377 . So closing for those.