[#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_space.go

@@ -49,10 +49,7 @@ type ResAnnounceSpace struct {
 //   - global (see Client docs).
 func (c *Client) ContainerAnnounceUsedSpace(ctx context.Context, prm PrmAnnounceSpace) (*ResAnnounceSpace, error) {
 	// check parameters
-	switch {
-	case ctx == nil:
-		return nil, errorMissingContext
-	case len(prm.announcements) == 0:
+	if len(prm.announcements) == 0 {
 		return nil, errorMissingAnnouncements
 	}