Do not reject entire observations based on gas or token price

[matYang]

Motivation

Removal of static token price changes a node’s view of destTokens. The prices reported by nodes that accepted new job specs will contain fewer tokens than the prices reported by nodes that haven’t, each release will reject the observations from the other.

Solution

Do not reject entire observations based on price. Prices being valid in an observation does not increase trustworthiness of its interval.

Instead, we can reject a token if len(not_nil(obs[token])l) < f + 1.
Reasons:

1. If len(not_nil(obs[token])) >= f + 1, then [1, f+1] honest node has included the token, therefore we know this is a legit token
2. Knowing this is a legit token, taking the median of prices aggregated from 2f+1 obs is sufficient to guard against f faults.
3. Validation cannot require more than f + 1 obs, that’d allow <f faulty nodes to halt price reporting for the token