fix: eth: remove trace sanity check

[Stebalien]

Proposed Changes

We added this check as a self-test to make sure that the message indices in our trace matched up with those in the block. Unfortunately, this only works for blocks on the main-chain, and breaks tracing of uncle blocks (and tracing of head).

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[Stebalien]

Hm. Apparently we're hitting this check in production. I'll have to debug this.

[Stebalien]

Nevermind, this code was the problem. We are attempting to lookup the parent messages by looking up the "next" epoch's tipset, then looking backwards. But, if we have a null tipset, we'd look up the wrong tipset.

So, removing this code is the correct thing to do.

[hawkaa]

LGTM!

[fridrik01]

@Stebalien So this failed when we were tracing a block which following tipset was a null tipset? Could we have a method for fetching the next non-null tipset for a given epoch (it may be useful in other cases) and then we could have sanity checks like this

[Stebalien]

@fridrik01 this logic doesn't work in the presence of forks either. E.g.:

Given:

A <- B <- C     <-- C is head
 \
  \- X <- Y     <-- fork

If we try to trace X, we'll end up looking up C as the next block instead of Y.