Shouldn't warn unused param for proof

[tanishiking]

Minimal Reproducible code

trait Proofs {
  def f[A, B](implicit ev: A =:= B) = 42
  def g[A, B](implicit ev: A <:< B) = 42
  def f2[A, B](ev: A =:= B) = 42
  def g2[A, B](ev: A <:< B) = 42
}

Expected behavior

Maybe we should suppress error if the type contains something like =:=