archive/zip: use proper doc comment for Deprecated notes

archive/zip: use proper doc comment for Deprecated notes

End-of-line comments are not doc comments,
so Deprecated notes in them are not recognized
as deprecation notices. Rewrite the comments.

Change-Id: Idc4681924f9a7e9ead62f672ef8a763e70db1f0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/453616
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>