Get rid of Sized from APIs

[alejandrohdezma]

🚀 What's included in this PR?

This PR removes the need to use Sized to check at compile time the size of parameters in the labels method. This is done by changing the method's signature from:

def labels[B, N <: Nat](labelNames: Sized[IndexedSeq[Label.Name], N])(
   f: B => Sized[IndexedSeq[String], N]
): LabelsBuildStep[F, A, B, N, L]

to...

def labels[B](labels: (Label.Name, B => String)*): LabelsBuildStep[F, A, B, L]

[janstenpickle]