update book code

eBook/exercises/chapter_7/remove_slice.go

@@ -0,0 +1,19 @@
+// remove_slice.go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	s := []string{"M", "N", "O", "P", "Q", "R"}
+	res := RemoveStringSlice(s, 2, 4) 
+	fmt.Println(res)  // [M N Q R]
+}
+
+func RemoveStringSlice(slice []string, start, end int) []string {
+    result := make([]string, len(slice) - (end - start))
+    at := copy(result, slice[:start])
+    copy(result[at:], slice[end:])
+	return result
+}