doc/mem: remove unnecessary pre tags within same snippet
doc/mem: remove unnecessary pre tags within same snippet

currently the snippet is segmented but should be one code snippet.

Change-Id: Ic747faf9bb1b52f9d1786eca70616a05b71ee801
Reviewed-on: https://go-review.googlesource.com/c/go/+/211198
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

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