remove garbage.

SliceTricks.md

@@ -29,12 +29,6 @@ a = append(a[:i], a[i+1:]...)
 a = a[:i+copy(a[i:], a[i+1:])]
 ```
 
-#### Delete without preserving order
-```go
-a[i] = a[len(a)-1] 
-a = a[:len(a)-1]
-
-```
 **NOTE** If the type of the element is a _pointer_ or a struct with pointer fields, which need to be garbage collected, the above implementations of ` Cut ` and ` Delete ` have a potential _memory leak_ problem: some elements with values are still referenced by slice ` a ` and thus can not be collected. The following code can fix this problem:
 > **Cut**
 ```go