XO0703: effect declared in `uses` is never performed

Reported by xo vet as a warning, never by xo check. Declaring more effects than the body performs is allowed, for example to keep an interface or a pub API stable while its implementation changes (core 6.2). Unless that is the intent, the extra effect overstates what the function can do and forces callers to declare it too. Remove it, or keep it deliberately.

Example

pub fn now(c: Clock) -> Time uses clock, net {
  c.now()
}

Fix

pub fn now(c: Clock) -> Time uses clock {
  c.now()
}

Run xo explain XO0703 for this text in a terminal, or see section 10.6 of the specification.