runtime/trace: remove remaining NewContext reference
runtime/trace: remove remaining NewContext reference

This is a documentation error.

Change-Id: I083021f151f7e80a0b9083b98452ae1f5920640d
Reviewed-on: https://go-review.googlesource.com/115598
Reviewed-by: Peter Weinberger <dd140fb9530d791057dd8833ea6768ff65fcde71@google.com>

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