[#48] client: Remove ctx == nil checks

Much less useful after we made context to be passed explicitly.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

client/container_delete.go

@@ -72,10 +72,7 @@ type ResContainerDelete struct {
 //   - global (see Client docs).
 func (c *Client) ContainerDelete(ctx context.Context, prm PrmContainerDelete) (*ResContainerDelete, error) {
 	// check parameters
-	switch {
-	case ctx == nil:
-		return nil, errorMissingContext
-	case !prm.idSet:
+	if !prm.idSet {
 		return nil, errorMissingContainer
 	}