_content/doc/tutorial: remove unused import "time"

`Time` was used by `math/rand.Seed` that is removed

Change-Id: I1d288694c5a92fb866d629d8de3d3cdfa79bbf48
GitHub-Last-Rev: 1485d39c3c
GitHub-Pull-Request: golang/website#226
Reviewed-on: https://go-review.googlesource.com/c/website/+/497835
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

_content/doc/tutorial/greetings-multiple-people.html

@@ -40,7 +40,6 @@ import (
     "errors"
     "fmt"
     "math/rand"
-    "time"
 )
 
 // Hello returns a greeting for the named person.