text/tabwriter: remove internal use of bytes.Buffer (cleanup)
text/tabwriter: remove internal use of bytes.Buffer (cleanup)

Noticed that we can simply use a []byte slice while investigating
a separate issue. Did the obvious simplification.

Change-Id: I921ebbb42135b5f1a10109236ceb9ae6e94ae7e2
Reviewed-on: https://go-review.googlesource.com/104757
Run-TryBot: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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