doc/go1.15: remove draft notice
doc/go1.15: remove draft notice

Updates #37419

Change-Id: I945fd1f8d87b15cf3143808dc68021b38531297d
Reviewed-on: https://go-review.googlesource.com/c/go/+/247772
Run-TryBot: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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