vendor: Update containerd to 1.6.1

Let's bring in the latest release of Containerd, 1.6.1, released on
March 2nd, 2022.

With this, we take the opportunity to remove containerd/api reference as
we shouldn't need a separate module only for the API.

Here's the list of changes needed in the code due to the bump:
* stop using `grpc.WithInsecure()` as it's been deprecated
  - use `grpc.WithTransportCredentials(insecure.NewCredentials())`
    instead

Fixes: #3820

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>

src/runtime/vendor/github.com/prometheus/procfs/zoneinfo.go

@@ -99,7 +99,6 @@ func parseZoneinfo(zoneinfoData []byte) ([]Zoneinfo, error) {
 				continue
 			}
 			if strings.HasPrefix(strings.TrimSpace(line), "per-node stats") {
-				zoneinfoElement.Zone = ""
 				continue
 			}
 			parts := strings.Fields(strings.TrimSpace(line))