vendor.conf: pin branches to releases or commits

Most of the dependencies have been copied from libpod's vendor.conf
where such a cleanup has been executed recently.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

vendor/github.com/docker/go-metrics/helpers.go

@@ -1,10 +0,0 @@
-package metrics
-
-func sumFloat64(vs ...float64) float64 {
-	var sum float64
-	for _, v := range vs {
-		sum += v
-	}
-
-	return sum
-}