crypto/tls: delete dead code curveIDForCurve

This unexported function has no call-sites.

Change-Id: I27a2cd231e4b8762b0d9e2dbd3d8ddd5b87fd5cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/673755
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
TryBot-Bypass: Daniel McCarney <daniel@binaryparadox.net>

src/crypto/tls/key_schedule.go

@@ -82,18 +82,3 @@ func curveForCurveID(id CurveID) (ecdh.Curve, bool) {
 		return nil, false
 	}
 }
-
-func curveIDForCurve(curve ecdh.Curve) (CurveID, bool) {
-	switch curve {
-	case ecdh.X25519():
-		return X25519, true
-	case ecdh.P256():
-		return CurveP256, true
-	case ecdh.P384():
-		return CurveP384, true
-	case ecdh.P521():
-		return CurveP521, true
-	default:
-		return 0, false
-	}
-}