Remove the runtime lock

This primarily served to protect us against shutting down the
Libpod runtime while operations (like creating a container) were
happening. However, it was very inconsistently implemented (a lot
of our longer-lived functions, like pulling images, just didn't
implement it at all...) and I'm not sure how much we really care
about this very-specific error case?

Removing it also removes a lot of potential deadlocks, which is
nice.

[NO NEW TESTS NEEDED]

Signed-off-by: Matthew Heon <mheon@redhat.com>

libpod/networking_linux.go

@@ -320,7 +320,7 @@ func (r *RootlessNetNS) Cleanup(runtime *Runtime) error {
 		// only if the netns is empty we know that we do not need cleanup
 		return c.state.NetNS != nil
 	}
-	ctrs, err := runtime.GetContainersWithoutLock(activeNetns)
+	ctrs, err := runtime.GetContainers(activeNetns)
 	if err != nil {
 		return err
 	}