Remove NextValidatorSet from the IBC Header

[AdityaSripal]

Description

Removes NextValidatorSet from the Header and uses the current ValidatorSet of the lastHeader as trustedValSet in the lite.Verify function. This will make the relayer a lot simpler and less bug-prone

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[cwgoes]

I can see how this makes things simpler. I think it will mean that we give up a bit of efficiency under bisection, right, since we're using a validator set one block behind the one we can actually trust? Are we concerned about that or not? (probably not too much)

[melekes]

👍

[cwgoes]

ACK modulo minor question

[cwgoes]

What does this change have to do with this PR?

[AdityaSripal]

Believe this is something @jackzampolin wanted to remove that annoying warning notice whenever you build sdk on Mac

[cwgoes]

Is the test-cover failure something we need to be concerned about?

[AdityaSripal]

Closed since #5764 incorporates these changes