doc/go1.15: remove encoding/xml doc
doc/go1.15: remove encoding/xml doc

The change is rolled back in CL 240179.

For #35151
For #39876

Change-Id: Id26ccbdb482772ac31c642156a9900102397b043
Reviewed-on: https://go-review.googlesource.com/c/go/+/240012
Reviewed-by: Alberto Donizetti <90b16103a35511ced020676f3544f17117fb4c92@gmail.com>
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

golang/go,golang/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,nawawi/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,cloudflare/go,golang/go