cmd/go: remove MallocNanoZone environment variable workaround
cmd/go: remove MallocNanoZone environment variable workaround

We added a workaround in runtime/race. This should not be
necessary now.

Updates #49138.

Change-Id: Ia2010e4acc95c4ddf5f463ab2919401d893c0bac
Reviewed-on: https://go-review.googlesource.com/c/go/+/374314
Trust: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Run-TryBot: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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