Stop allowing clippy::derive-partial-eq-without-eq and fix warnings
about deriving PartialEq without also deriving Eq.
In one case I removed the PartialEq because it a) wasn't necessary,
and b) sketchy because it was comparing floating point numbers.
IMO, that's a good argument for enforcing the lint rule, because it
would most likely have been caught during review if it had been enabled.
