etcd: remove unnecessary iterator step from cursor Delete

The etcd cursor Delete stepped to the next item in the range before
Delete to not invalidate the iteation. This is unnecessary and not
compatible with bbolt, resulting in an extra fetch too.

kvdb/etcd/readwrite_cursor.go

@@ -116,23 +116,11 @@ func (c *readWriteCursor) Seek(seek []byte) (key, value []byte) {
 // invalidating the cursor.  Returns ErrIncompatibleValue if attempted
 // when the cursor points to a nested bucket.
 func (c *readWriteCursor) Delete() error {
-	// Get the next key after the current one. We could do this
-	// after deletion too but it's one step more efficient here.
-	nextKey, err := c.bucket.tx.stm.Next(c.prefix, c.currKey)
-	if err != nil {
-		return err
-	}
-
 	if isBucketKey(c.currKey) {
 		c.bucket.DeleteNestedBucket(getKey(c.currKey))
 	} else {
 		c.bucket.Delete(getKey(c.currKey))
 	}
 
-	if nextKey != nil {
-		// Set current key to the next one.
-		c.currKey = nextKey.key
-	}
-
 	return nil
 }